Tactics¶
A deduction rule is a link between some (unique) formula, that we call the conclusion and (several) formulas that we call the premises. A deduction rule can be read in two ways. The first one says: “if I know this and this then I can deduce this”. For instance, if I have a proof of A and a proof of B then I have a proof of A ∧ B. This is forward reasoning from premises to conclusion. The other way says: “to prove this I have to prove this and this”. For instance, to prove A ∧ B, I have to prove A and I have to prove B. This is backward reasoning from conclusion to premises. We say that the conclusion is the goal to prove and premises are the subgoals. The tactics implement backward reasoning. When applied to a goal, a tactic replaces this goal with the subgoals it generates. We say that a tactic reduces a goal to its subgoal(s).
Each (sub)goal is denoted with a number. The current goal is numbered 1. By default, a tactic is applied to the current goal, but one can address a particular goal in the list by writing n:tactic which means “apply tactic tactic to goal number n”. We can show the list of subgoals by typing Show (see Section Requesting information).
Since not every rule applies to a given statement, every tactic cannot be used to reduce any goal. In other words, before applying a tactic to a given goal, the system checks that some preconditions are satisfied. If it is not the case, the tactic raises an error message.
Tactics are built from atomic tactics and tactic expressions (which extends the folklore notion of tactical) to combine those atomic tactics. This chapter is devoted to atomic tactics. The tactic language will be described in Chapter The tactic language.
Invocation of tactics¶
A tactic is applied as an ordinary command. It may be preceded by a goal selector (see Section Semantics). If no selector is specified, the default selector is used.
tactic_invocation ::= toplevel_selector : tactic. tactic .

Option
Default Goal Selector toplevel_selector
¶ This option controls the default selector – used when no selector is specified when applying a tactic – is set to the chosen value. The initial value is 1, hence the tactics are, by default, applied to the first goal. Using value
all
will make is so that tactics are, by default, applied to every goal simultaneously. Then, to apply a tactic tac to the first goal only, you can write1:tac
. Although more selectors are available, onlyall
or a single natural number are valid default goal selectors.
Bindings list¶
Tactics that take a term as argument may also support a bindings list,
so as to instantiate some parameters of the term by name or position.
The general form of a term equipped with a bindings list is term with
bindings_list
where bindings_list
may be of two different forms:
In a bindings list of the form
(ref:= term)*
,ref
is either anident
or anum
. The references are determined according to the type ofterm
. Ifref
is an identifier, this identifier has to be bound in the type ofterm
and the binding provides the tactic with an instance for the parameter of this name. Ifref
is some numbern
, this number denotes then
th non dependent premise of theterm
, as determined by the type ofterm
.
Error
No such binder
¶

Error
A bindings list can also be a simple list of terms
term*
. In that case the references to which these terms correspond are determined by the tactic. In case ofinduction
,destruct
,elim
andcase
(see The tactic language) the terms have to provide instances for all the dependent products in the type of term while in the case ofapply
, or ofconstructor
and its variants, only instances for the dependent products that are not bound in the conclusion of the type are required.
Error
Not the right number of missing arguments.
¶

Error
Occurrences sets and occurrences clauses¶
An occurrences clause is a modifier to some tactics that obeys the following syntax:
occurence_clause ::= ingoal_occurences
goal_occurences ::= [ident [at_occurences
], ... , ident [at_occurences
] [ [* [at_occurences
]]]]  *  [* [at_occurences
]]  * at_occurrences ::= atoccurrences
occurences ::= []num
...num
The role of an occurrence clause is to select a set of occurrences of a term in
a goal. In the first case, the ident at num*?
parts indicate that
occurrences have to be selected in the hypotheses named ident
. If no
numbers are given for hypothesis ident
, then all the occurrences of term
in the hypothesis are selected. If numbers are given, they refer to occurrences
of term when the term is printed using option Printing All
, counting
from left to right. In particular, occurrences of term in implicit arguments
(see Implicit arguments) or coercions (see Coercions) are counted.
If a minus sign is given between at and the list of occurrences, it negates the condition so that the clause denotes all the occurrences except the ones explicitly mentioned after the minus sign.
As an exception to the lefttoright order, the occurrences in thereturn subexpression of a match are considered before the occurrences in the matched term.
In the second case, the *
on the left of 
means that all occurrences
of term are selected in every hypothesis.
In the first and second case, if *
is mentioned on the right of 
, the
occurrences of the conclusion of the goal have to be selected. If some numbers
are given, then only the occurrences denoted by these numbers are selected. If
no numbers are given, all occurrences of term
in the goal are selected.
Finally, the last notation is an abbreviation for *  *
. Note also
that 
is optional in the first case when no *
is given.
Here are some tactics that understand occurrences clauses: set
, remember
, induction
, destruct
.
See also: Managing the local context, Case analysis and induction, Printing constructions in full.
Applying theorems¶
This tactic applies to any goal. It gives directly the exact proof
term of the goal. Let T
be our goal, let p
be a term of type U
then
exact p
succeeds iff T
and U
are convertible (see
Conversion rules).

Error
Not an exact proof.
¶
This tactic behaves like exact but is able to handle terms and goals with metavariables.

assumption
¶
This tactic looks in the local context for an hypothesis which type is equal to the goal. If it is the case, the subgoal is proved. Otherwise, it fails.

Error
No such assumption.
¶

Variant
eassumption
¶
This tactic behaves like assumption but is able to handle goals with metavariables.
This tactic applies to any goal. It behaves like exact with a big
difference: the user can leave some holes (denoted by _
or``(_:type)``) in
the term. refine will generate as many subgoals as there are holes in
the term. The type of holes must be either synthesized by the system
or declared by an explicit cast like (_:nat>Prop)
. Any subgoal that
occurs in other subgoals is automatically shelved, as if calling
shelve_unifiable (see Section 8.17.4). This lowlevel tactic can be
useful to advanced users.
Example
 Inductive Option : Set :=  Fail : Option  Ok : bool > Option.
 Option is defined Option_rect is defined Option_ind is defined Option_rec is defined
 Definition get : forall x:Option, x <> Fail > bool.
 1 subgoal ============================ forall x : Option, x <> Fail > bool
 refine (fun x:Option => match x return x <> Fail > bool with  Fail => _  Ok b => fun _ => b end).
 1 subgoal x : Option ============================ Fail <> Fail > bool
 intros; absurd (Fail = Fail); trivial.
 No more subgoals.
 Defined.
 get is defined

Error
invalid argument
¶ The tactic
refine
does not know what to do with the term you gave.

Error
Refine passed illformed term
¶ The term you gave is not a valid proof (not easy to debug in general). This message may also occur in higherlevel tactics that call
refine
internally.

Error
Cannot infer a term for this placeholder
¶ There is a hole in the term you gave which type cannot be inferred. Put a cast around it.

Variant
simple refine term
¶ This tactic behaves like refine, but it does not shelve any subgoal. It does not perform any betareduction either.

Variant
notypeclasses refine term
This tactic behaves like
refine
except it performs typechecking without resolution of typeclasses.

Variant
simple notypeclasses refine term
¶ This tactic behaves like
simple refine
except it performs typechecking without resolution of typeclasses.
This tactic applies to any goal. The argument term is a term wellformed in the local context. The tactic apply tries to match the current goal against the conclusion of the type of term. If it succeeds, then the tactic returns as many subgoals as the number of nondependent premises of the type of term. If the conclusion of the type of term does not match the goal and the conclusion is an inductive type isomorphic to a tuple type, then each component of the tuple is recursively matched to the goal in the lefttoright order.
The tactic apply
relies on firstorder unification with dependent types
unless the conclusion of the type of term
is of the form P (t
_{1}
…
t
_{n} )
with P to be instantiated. In the latter case, the behavior
depends on the form of the goal. If the goal is of the form
(fun x => Q) u
_{1} …
u
_{n} and the t
_{i} and
u
_{i} unifies, then P
is taken to be (fun x => Q)
. Otherwise,
apply
tries to define P
by abstracting over t
_{1} …
t
_{n} in the goal. See pattern
to transform the goal so that it
gets the form (fun x => Q) u
_{1} …
u
_{n}.

Error
Unable to unify … with … .
¶
The apply tactic failed to match the conclusion of term and the current goal.
You can help the apply tactic by transforming your goal with the
change
or pattern
tactics.
This occurs when some instantiations of the premises of term are not deducible from the unification. This is the case, for instance, when you want to apply a transitivity property. In this case, you have to use one of the variants below:
Provides apply with explicit instantiations for all dependent premises of the
type of term that do not occur in the conclusion and consequently cannot be
found by unification. Notice that the collection term+
must be given
according to the order of these dependent premises of the type of term.

Error
Not the right number of missing arguments.

Variant
apply term with bindings_list
This also provides apply with values for instantiating premises. Here, variables are referred by names and nondependent products by increasing numbers (see bindings list).

Variant
apply term+,
This is a shortcut for apply term
_{1}
; [..  ... ; [ ..  apply
term
_{n} ] ... ]
,
i.e. for the successive applications of term
_{i+1} on the last subgoal
generated by apply term
_{i} , starting from the application of
term
_{1}.
The tactic eapply
behaves like apply
but it does not fail when no
instantiations are deducible for some variables in the premises. Rather, it
turns these variables into existential variables which are variables still to
instantiate (see Existential variables). The instantiation is
intended to be found later in the proof.
This behaves like apply
but it reasons modulo conversion only on subterms
that contain no variables to instantiate. For instance, the following example
does not succeed because it would require the conversion of id ?foo
and
O
.
Example
 Definition id (x : nat) := x.
 id is defined
 Hypothesis H : forall y, id y = y.
 Toplevel input, characters 034: > Hypothesis H : forall y, id y = y. > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Warning: H is declared as a local axiom [localdeclaration,scope] H is declared
 Goal O = O.
 1 subgoal ============================ 0 = 0
 Fail simple apply H.
 The command has indeed failed with message: Unable to unify “id ?M160 = ?M160” with “0 = 0”.
Because it reasons modulo a limited amount of conversion, simple apply
fails
quicker than apply
and it is then wellsuited for uses in userdefined
tactics that backtrack often. Moreover, it does not traverse tuples as apply
does.

Variant
simple? apply term with bindings_list?+,

Variant
simple? eapply term with bindings_list?+,
¶
This summarizes the different syntaxes for apply
and eapply
.
This tactic applies to any goal, say G
. The argument term has to be
wellformed in the current context, its type being reducible to a nondependent
product A > B
with B
possibly containing products. Then it generates
two subgoals B>G
and A
. Applying lapply H
(where H
has type
A>B
and B
does not start with a product) does the same as giving the
sequence cut B. 2:apply H.
where cut
is described below.

Warning
When term contains more than one non dependent product the tactic lapply only takes into account the first product.
¶
Example
Assume we have a transitive relation R
on nat
:
 Variable R : nat > nat > Prop.
 Toplevel input, characters 032: > Variable R : nat > nat > Prop. > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Warning: R is declared as a local axiom [localdeclaration,scope] R is declared
 Hypothesis Rtrans : forall x y z:nat, R x y > R y z > R x z.
 Toplevel input, characters 062: > Hypothesis Rtrans : forall x y z:nat, R x y > R y z > R x z. > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Warning: Rtrans is declared as a local axiom [localdeclaration,scope] Rtrans is declared
 Variables n m p : nat.
 Toplevel input, characters 022: > Variables n m p : nat. > ^^^^^^^^^^^^^^^^^^^^^^ Warning: n is declared as a local axiom [localdeclaration,scope] n is declared Toplevel input, characters 022: > Variables n m p : nat. > ^^^^^^^^^^^^^^^^^^^^^^ Warning: m is declared as a local axiom [localdeclaration,scope] m is declared Toplevel input, characters 022: > Variables n m p : nat. > ^^^^^^^^^^^^^^^^^^^^^^ Warning: p is declared as a local axiom [localdeclaration,scope] p is declared
 Hypothesis Rnm : R n m.
 Toplevel input, characters 023: > Hypothesis Rnm : R n m. > ^^^^^^^^^^^^^^^^^^^^^^^ Warning: Rnm is declared as a local axiom [localdeclaration,scope] Rnm is declared
 Hypothesis Rmp : R m p.
 Toplevel input, characters 023: > Hypothesis Rmp : R m p. > ^^^^^^^^^^^^^^^^^^^^^^^ Warning: Rmp is declared as a local axiom [localdeclaration,scope] Rmp is declared
Consider the goal (R n p)
provable using the transitivity of R
:
 Goal R n p.
 1 subgoal ============================ R n p
The direct application of Rtrans
with apply
fails because no value
for y
in Rtrans
is found by apply
:
 Fail apply Rtrans.
 The command has indeed failed with message: Unable to find an instance for the variable y.
A solution is to apply (Rtrans n m p)
or (Rtrans n m)
.
 apply (Rtrans n m p).
 2 subgoals ============================ R n m subgoal 2 is: R m p
Note that n
can be inferred from the goal, so the following would work
too.
 apply (Rtrans _ m).
 2 subgoals ============================ R n m subgoal 2 is: R m p
More elegantly, apply Rtrans with (y:=m)
allows only mentioning the
unknown m:
 apply Rtrans with (y := m).
 2 subgoals ============================ R n m subgoal 2 is: R m p
Another solution is to mention the proof of (R x y)
in Rtrans
 apply Rtrans with (1 := Rnm).
 1 subgoal ============================ R m p
… or the proof of (R y z)
.
 apply Rtrans with (2 := Rmp).
 1 subgoal ============================ R n m
On the opposite, one can use eapply
which postpones the problem of
finding m
. Then one can apply the hypotheses Rnm
and Rmp
. This
instantiates the existential variable and completes the proof.
 eapply Rtrans.
 2 focused subgoals (shelved: 1) ============================ R n ?y subgoal 2 is: R ?y p
 apply Rnm.
 1 subgoal ============================ R m p
 apply Rmp.
 No more subgoals.
Note
When the conclusion of the type of the term to apply
is an inductive
type isomorphic to a tuple type and apply
looks recursively whether a
component of the tuple matches the goal, it excludes components whose
statement would result in applying an universal lemma of the form
forall A, ... > A
. Excluding this kind of lemma can be avoided by
setting the following option:

Option
Universal Lemma Under Conjunction
¶ This option, which preserves compatibility with versions of Coq prior to 8.4 is also available for
apply term in ident
(seeapply ... in
).

apply term in ident
¶ This tactic applies to any goal. The argument
term
is a term wellformed in the local context and the argumentident
is an hypothesis of the context. The tacticapply term in ident
tries to match the conclusion of the type ofident
against a nondependent premise of the type ofterm
, trying them from right to left. If it succeeds, the statement of hypothesisident
is replaced by the conclusion of the type ofterm
. The tactic also returns as many subgoals as the number of other nondependent premises in the type ofterm
and of the nondependent premises of the type ofident
. If the conclusion of the type ofterm
does not match the goal and the conclusion is an inductive type isomorphic to a tuple type, then the tuple is (recursively) decomposed and the first component of the tuple of which a nondependent premise matches the conclusion of the type ofident
. Tuples are decomposed in a widthfirst lefttoright order (for instance if the type ofH1
is aA <> B
statement, and the type ofH2
isA
thenapply H1 in H2
transforms the type ofH2
intoB
). The tacticapply
relies on firstorder patternmatching with dependent types.

Error
Statement without assumptions.
¶ This happens if the type of
term
has no non dependent premise.

Error
Unable to apply.
¶ This happens if the conclusion of
ident
does not match any of the non dependent premises of the type ofterm
.

Variant
apply term with bindings_list+, in ident
This does the same but uses the bindings in each
(id := @ val)
to instantiate the parameters of the corresponding type ofterm
(see bindings list).

Variant
eapply term with bindings_list+, in ident
This works as
apply ... in
but turns unresolved bindings into existential variables, if any, instead of failing.

Variant
apply term with bindings_list+, in ident as intro_pattern
¶ This works as
apply ... in
then applies theintro_pattern
to the hypothesisident
.

Variant
eapply term with bindings_list+, in ident as intro_pattern.
This works as
apply ... in as
but usingeapply
.

Variant
simple apply term in ident
This behaves like
apply ... in
but it reasons modulo conversion only on subterms that contain no variables to instantiate. For instance, ifid := fun x:nat => x
andH: forall y, id y = y > True
andH0 : O = O
thensimple apply H in H0
does not succeed because it would require the conversion ofid ?1234
andO
where?1234
is a variable to instantiate. Tacticsimple apply term in ident
does not either traverse tuples asapply term in ident
does.

Variant
simple? apply term with bindings_list?+, in ident as intro_pattern?

Variant
simple? eapply term with bindings_list?+, in ident as intro_pattern?
This summarizes the different syntactic variants of
apply term in ident
andeapply term in ident
.

constructor num
¶ This tactic applies to a goal such that its conclusion is an inductive type (say
I
). The argumentnum
must be less or equal to the numbers of constructor(s) ofI
. Letc
_{i} be the ith constructor ofI
, thenconstructor i
is equivalent tointros; apply c
_{i}.

Error
Not an inductive product
¶

Error
Not enough constructors
¶

Variant
constructor
This tries
constructor
_{1} thenconstructor
_{2}, …, thenconstructor
_{n} where n is the number of constructors of the head of the goal.

Variant
constructor num with bindings_list
 Let
c
be the ith constructor ofI
, thenconstructor i with bindings_list
is equivalent tointros; apply c with bindings_list
.
Warning
The terms in the bindings_list are checked in the context where constructor is executed and not in the context where apply is executed (the introductions are not taken into account).
¶

Warning

Variant
split
¶ This applies only if
I
has a single constructor. It is then equivalent toconstructor 1.
. It is typically used in the case of a conjunctionA
\(\wedge\)B
.

Error
Not an inductive goal with 1 constructor
¶

Variant
exists val
¶ This applies only if
I
has a single constructor. It is then equivalent tointros; constructor 1 with bindings_list.
It is typically used in the case of an existential quantification \(\exists\)x, P(x).

Error
Not an inductive goal with 1 constructor

Variant
exists bindings_list
This iteratively applies
exists bindings_list
.

Variant
left
¶

Variant
right
¶ These tactics apply only if
I
has two constructors, for instance in the case of a disjunctionA
\(\vee\)B
. Then, they are respectively equivalent toconstructor 1
andconstructor 2
.

Error
Not an inductive goal with 2 constructors
¶

Variant
left with bindings_list

Variant
right with bindings_list

Variant
split with bindings_list
As soon as the inductive type has the right number of constructors, these expressions are equivalent to calling
constructor i with bindings_list
for the appropriatei
.

Variant
econstructor
¶

Variant
eexists
¶

Variant
esplit
¶

Variant
eleft
¶
Managing the local context¶

intro
¶
This tactic applies to a goal that is either a product or starts with a let binder. If the goal is a product, the tactic implements the “Lam” rule given in Typing rules [1]. If the goal starts with a let binder, then the tactic implements a mix of the “Let” and “Conv”.
If the current goal is a dependent product \(\forall\) x:T, U
(resp
let x:=t in U
) then intro
puts x:T
(resp x:=t
) in the local
context. The new subgoal is U
.
If the goal is a nondependent product T
\(\rightarrow\)U
, then it
puts in the local context either Hn:T
(if T
is of type Set
or
Prop
) or Xn:T (if the type of T
is Type
). The optional index
n
is such that Hn
or Xn
is a fresh identifier. In both cases, the
new subgoal is U
.
If the goal is neither a product nor starting with a let definition,
the tactic intro
applies the tactic hnf
until the tactic intro
can
be applied or the goal is not headreducible.

Error
No product even after headreduction.
¶

Variant
intros
This repeats
intro
until it meets the headconstant. It never reduces headconstants and it never fails.

intro @ident
This applies
intro
but forcesident
to be the name of the introduced hypothesis.
Note
If a name used by intro hides the base name of a global constant then the latter can still be referred to by a qualified name (see Qualified names).

Variant
intros ident+.
This is equivalent to the composed tactic
intro ident; … ; intro ident
. More generally, theintros
tactic takes a pattern as argument in order to introduce names for components of an inductive definition or to clear introduced hypotheses. This is explained in Managing the local context.

Variant
intros until ident
This repeats intro until it meets a premise of the goal having form (@ident:term) and discharges the variable named ident of the current goal.

Error
No such hypothesis in current goal
¶

Variant
intros until num
This repeats intro until the numth nondependent product. For instance, on the subgoal
forall x y:nat, x=y > y=x
the tacticintros until 1
is equivalent tointros x y H
, asx=y > y=x
is the first nondependent product. And on the subgoalforall x y z:nat, x=y > y=x
the tacticintros until 1
is equivalent tointros x y z
as the product onz
can be rewritten as a nondependent product:forall x y:nat, nat > x=y > y=x

Error
No such hypothesis in current goal.
This happens when num is 0 or is greater than the number of nondependent products of the goal.

Variant
intro after ident

Variant
intro before ident

Variant
intro at top

Variant
intro at bottom
These tactics apply
intro
and move the freshly introduced hypothesis respectively after the hypothesisident
, before the hypothesisident
, at the top of the local context, or at the bottom of the local context. All hypotheses on which the new hypothesis depends are moved too so as to respect the order of dependencies between hypotheses. Note thatintro at bottom
is a synonym forintro
with no argument.

Variant
intro ident at top

Variant
intro ident at bottom
These tactics behave as previously but naming the introduced hypothesis
ident
. It is equivalent tointro ident
followed by the appropriate call to move (seemove ... after
).

intros intro_pattern_list
¶ This extension of the tactic
intros
allows to apply tactics on the fly on the variables or hypotheses which have been introduced. An introduction pattern listintro_pattern_list
is a list of introduction patterns possibly containing the filling introduction patterns * and **. An introduction pattern is either: a naming introduction pattern, i.e. either one of:
 the pattern
?
 the pattern
?ident
 an identifier
 the pattern
 an action introduction pattern which itself classifies into:
 a disjunctive/conjunctive introduction pattern, i.e. either one of
 a disjunction of lists of patterns
[intro_pattern_list  …  intro_pattern_list]
 a conjunction of patterns:
(p+,)
 a list of patterns
(p+&)
for sequence of rightassociative binary constructs
 a disjunction of lists of patterns
 an equality introduction pattern, i.e. either one of:
 a pattern for decomposing an equality:
[= p+]
 the rewriting orientations:
>
or<
 a pattern for decomposing an equality:
 the onthefly application of lemmas:
p%term+
wherep
itself is not a pattern for onthefly application of lemmas (note: syntax is in experimental stage)
 a disjunctive/conjunctive introduction pattern, i.e. either one of
 the wildcard:
_
Assuming a goal of type
Q → P
(nondependent product), or of type \(\forall\)x:T, P
(dependent product), the behavior ofintros p
is defined inductively over the structure of the introduction patternp
: a naming introduction pattern, i.e. either one of:
Introduction on ?
performs the introduction, and lets Coq choose a fresh
name for the variable;
Introduction on ?ident
performs the introduction, and lets Coq choose a
fresh name for the variable based on ident
;
Introduction on ident
behaves as described in intro
Introduction over a disjunction of list of patterns
[intro_pattern_list  …  intro_pattern_list ]
expects the product
to be over an inductive type whose number of constructors is n (or more
generally over a type of conclusion an inductive type built from n
constructors, e.g. C > A\/B
with n=2 since A\/B
has 2
constructors): it destructs the introduced hypothesis as destruct
(see
destruct
) would and applies on each generated subgoal the
corresponding tactic;

Variant
intros intro_pattern_list
The introduction patterns in
intro_pattern_list
are expected to consume no more than the number of arguments of the ith constructor. If it consumes less, then Coq completes the pattern so that all the arguments of the constructors of the inductive type are introduced (for instance, the list of patterns[  ] H
applied on goalforall x:nat, x=0 > 0=x
behaves the same as the list of patterns[  ? ] H
);
Introduction over a conjunction of patterns (p+,)
expects
the goal to be a product over an inductive type I
with a single
constructor that itself has at least n arguments: It performs a case
analysis over the hypothesis, as destruct
would, and applies the
patterns p+
to the arguments of the constructor of I
(observe
that (p+)
is an alternative notation for [p+]
);
Introduction via (p+&)
is a shortcut for introduction via
(p,( … ,( …, p ) … ))
; it expects the hypothesis to be a sequence of
rightassociative binary inductive constructors such as conj
or
ex_intro
; for instance, an hypothesis with type
A /\(exists x, B /\ C /\ D)
can be introduced via pattern
(a & x & b & c & d)
;
If the product is over an equality type, then a pattern of the form
[= p+]
applies either injection
or discriminate
instead of destruct
; if injection
is applicable, the patterns
p+,
are used on the hypotheses generated by injection
; if the
number of patterns is smaller than the number of hypotheses generated, the
pattern ?
is used to complete the list;

Variant
introduction over >

Variant
introduction over <
expects the hypothesis to be an equality and the righthandside (respectively the lefthandside) is replaced by the lefthandside (respectively the righthandside) in the conclusion of the goal; the hypothesis itself is erased; if the term to substitute is a variable, it is substituted also in the context of goal and the variable is removed too;
Introduction over a pattern p%term+
first applies term+
on the hypothesis to be introduced (as in apply term+,
) prior to the
application of the introduction pattern p
;
Introduction on the wildcard depends on whether the product is dependent or not:
in the nondependent case, it erases the corresponding hypothesis (i.e. it
behaves as an intro
followed by a clear
) while in the
dependent case, it succeeds and erases the variable only if the wildcard is part
of a more complex list of introduction patterns that also erases the hypotheses
depending on this variable;
Introduction over *
introduces all forthcoming quantified variables
appearing in a row; introduction over **
introduces all forthcoming
quantified variables or hypotheses until the goal is not any more a
quantification or an implication.
Example
 Goal forall A B C:Prop, A \/ B /\ C > (A > C) > C.
 1 subgoal ============================ forall A B C : Prop, A \/ B /\ C > (A > C) > C
 intros * [a  (_,c)] f.
 2 subgoals A, B, C : Prop a : A f : A > C ============================ C subgoal 2 is: C
Note
intros p+
is not equivalent to intros p; … ; intros p
for the following reason: If one of the p
is a wildcard pattern, it
might succeed in the first case because the further hypotheses it
depends in are eventually erased too while it might fail in the second
case because of dependencies in hypotheses which are not yet
introduced (and a fortiori not yet erased).
Note
In intros intro_pattern_list
, if the last introduction pattern
is a disjunctive or conjunctive pattern
[intro_pattern_list+]
, the completion of intro_pattern_list
so that all the arguments of the ith constructors of the corresponding
inductive type are introduced can be controlled with the following option:

Option
Bracketing Last Introduction Pattern
¶ Force completion, if needed, when the last introduction pattern is a disjunctive or conjunctive pattern (on by default).

clear ident
¶ This tactic erases the hypothesis named
ident
in the local context of the current goal. As a consequence,ident
is no more displayed and no more usable in the proof development.

Error
No such hypothesis.
¶

Variant
clearbody ident
¶ This tactic expects
ident
to be a local definition then clears its body. Otherwise said, this tactic turns a definition into an assumption.

Variant
clear  ident+
This tactic clears all the hypotheses except the ones depending in the hypotheses named
ident+
and in the goal.

Variant
clear
This tactic clears all the hypotheses except the ones the goal depends on.

Variant
clear dependent ident
This clears the hypothesis
ident
and all the hypotheses that depend on it.
This applies to any goal with variables ident+
. It moves the hypotheses
(possibly defined) to the goal, if this respects dependencies. This tactic is
the inverse of intro
.

Error
No such hypothesis.

revert dependent @ident
This moves to the goal the hypothesis
ident
and all the hypotheses that depend on it.

move ident after ident
¶ This moves the hypothesis named
ident
in the local context after the hypothesis namedident
, where “after” is in reference to the direction of the move. The proof term is not changed.If
ident
comes beforeident
in the order of dependencies, then all the hypotheses betweenident
andident@
that (possibly indirectly) depend onident
are moved too, and all of them are thus moved afterident
in the order of dependencies.If
ident
comes afterident
in the order of dependencies, then all the hypotheses betweenident
andident
that (possibly indirectly) occur in the type ofident
are moved too, and all of them are thus moved beforeident
in the order of dependencies.

Variant
move ident before ident
This moves
ident
towards and just before the hypothesis namedident
. As formove ... after ...
, dependencies overident
(whenident
comes beforeident
in the order of dependencies) or in the type ofident
(whenident
comes afterident
in the order of dependencies) are moved too.

Variant
move ident at top
This moves
ident
at the top of the local context (at the beginning of the context).

Variant
move ident at bottom
This moves ident at the bottom of the local context (at the end of the context).

Error
No such hypothesis
Example
 Goal forall x :nat, x = 0 > forall z y:nat, y=y> 0=x.
 1 subgoal ============================ forall x : nat, x = 0 > nat > forall y : nat, y = y > 0 = x
 intros x H z y H0.
 1 subgoal x : nat H : x = 0 z, y : nat H0 : y = y ============================ 0 = x
 move x after H0.
 1 subgoal z, y : nat H0 : y = y x : nat H : x = 0 ============================ 0 = x
 Undo.
 1 subgoal x : nat H : x = 0 z, y : nat H0 : y = y ============================ 0 = x
 move x before H0.
 1 subgoal z, y, x : nat H : x = 0 H0 : y = y ============================ 0 = x
 Undo.
 1 subgoal x : nat H : x = 0 z, y : nat H0 : y = y ============================ 0 = x
 move H0 after H.
 1 subgoal x, y : nat H0 : y = y H : x = 0 z : nat ============================ 0 = x
 Undo.
 1 subgoal x : nat H : x = 0 z, y : nat H0 : y = y ============================ 0 = x
 move H0 before H.
 1 subgoal x : nat H : x = 0 y : nat H0 : y = y z : nat ============================ 0 = x
This renames hypothesis ident
into ident
in the current context.
The name of the hypothesis in the proofterm, however, is left unchanged.

Variant
rename ident into ident+,
This renames the variables
ident
intoident
in parallel. In particular, the target identifiers may contain identifiers that exist in the source context, as long as the latter are also renamed by the same tactic.

Error
No such hypothesis

Error
ident is already used

set (ident := term)
¶ This replaces
term
byident
in the conclusion of the current goal and adds the new definitionident := term
to the local context.If
term
has holes (i.e. subexpressions of the form “_”), the tactic first checks that all subterms matching the pattern are compatible before doing the replacement using the leftmost subterm matching the pattern.

Variant
set (ident := term ) in goal_occurrences
This notation allows specifying which occurrences of
term
have to be substituted in the context. Thein goal_occurrences
clause is an occurrence clause whose syntax and behavior are described in goal occurences.

Variant
set (ident binder+ := term )
This is equivalent to
set (ident := funbinder binder+ => term )
.

Variant
set term

Variant
This behaves as :n:`set(ident := term)` but :n:`ident` is generated by

Variant
Coq. This variant also supports an occurrence clause.

Variant
set term in goal_occurrences
These are the general forms that combine the previous possibilities.

Variant
eset term in goal_occurrences
¶ While the different variants of
set
expect that no existential variables are generated by the tactic,eset
removes this constraint. In practice, this is relevant only wheneset
is used as a synonym ofepose
, i.e. when the :@term does not occur in the goal.

Variant
remember term as ident
¶ This behaves as
set (ident:= term ) in *
and using a logical (Leibniz’s) equality instead of a local definition.

Variant
remember term as ident eqn:ident
This behaves as
remember term as ident
, except that the name of the generated equality is also given.

Variant
remember term as ident in goal_occurrences
This is a more general form of
remember
that remembers the occurrences of term specified by an occurrences set.

Variant
eremember term as ident eqn:ident
¶ While the different variants of
remember
expect that no existential variables are generated by the tactic,eremember
removes this constraint.

Variant
pose ( ident := term )
¶ This adds the local definition
ident := term
to the current context without performing any replacement in the goal or in the hypotheses. It is equivalent toset ( ident := term ) in 
.

Variant
pose ( ident binder+ := term )
This is equivalent to
pose (ident := funbinder binder+ => term)
.

Variant
epose term
¶ While the different variants of
pose
expect that no existential variables are generated by the tactic, epose removes this constraint.

decompose [qualid+] term
¶ This tactic recursively decomposes a complex proposition in order to obtain atomic ones.
Example
 Goal forall A B C:Prop, A /\ B /\ C \/ B /\ C \/ C /\ A > C.
 intros A B C H; decompose [and or] H; assumption.
 No more subgoals.
 Qed.
 Unnamed_thm1 is defined 1 subgoal x : nat H : x = 0 y : nat H0 : y = y z : nat ============================ 0 = x
decompose
does not work on righthand sides of implications or products.

Variant
decompose sum term
This decomposes sum types (like or).

Variant
decompose record term
This decomposes record types (inductive types with one constructor, like “and” and “exists” and those defined with the Record macro, see Record types).
Controlling the proof flow¶

assert (ident : form)
¶ This tactic applies to any goal.
assert (H : U)
adds a new hypothesis of nameH
assertingU
to the current goal and opens a new subgoalU
[2]. The subgoalU
comes first in the list of subgoals remaining to prove.

Error
Not a proposition or a type
¶ Arises when the argument form is neither of type
Prop
,Set
norType
.

Variant
assert form by tactic
This tactic behaves like
assert
but applies tactic to solve the subgoals generated by assert.
Error
Proof is not complete
¶

Error

Variant
assert form as intro_pattern
If
intro_pattern
is a naming introduction pattern (seeintro
), the hypothesis is named after this introduction pattern (in particular, ifintro_pattern
isident
, the tactic behaves likeassert (ident : form)
). Ifintro_pattern
is an action introduction pattern, the tactic behaves likeassert form
followed by the action done by this introduction pattern.

Variant
assert form as intro_pattern by tactic
This combines the two previous variants of
assert
.

Variant
assert (ident := term )
This behaves as
assert (ident : type) by exact term
wheretype
is the type ofterm
. This is deprecated in favor ofpose proof
. If the head of term isident
, the tactic behaves asspecialize term
.

Variant
eassert form as intro_pattern by tactic
¶

Variant
assert (ident := term)
While the different variants of
assert
expect that no existential variables are generated by the tactic,eassert
removes this constraint. This allows not to specify the asserted statement completeley before starting to prove it.

Variant
pose proof term as intro_pattern?
¶ This tactic behaves like
assert T as intro_pattern? by exact term
whereT
is the type ofterm
. In particular,pose proof term as ident
behaves asassert (ident := term)
andpose proof term as intro_pattern
is the same as applying the intro_pattern toterm
.

Variant
epose proof term as intro_pattern?
While
pose proof
expects that no existential variables are generated by the tactic,epose proof
removes this constraint.

Variant
enough (ident : form)
¶ This adds a new hypothesis of name
ident
assertingform
to the goal the tacticenough
is applied to. A new subgoal statingform
is inserted after the initial goal rather than before it asassert
would do.

Variant
enough form
This behaves like
enough (ident : form)
with the nameident
of the hypothesis generated by Coq.

Variant
enough form as intro_pattern
This behaves like
enough form
usingintro_pattern
to name or destruct the new hypothesis.

Variant
enough (ident : form) by tactic

Variant
enough form by tactic

Variant
enough form as intro_pattern by tactic
This behaves as above but with
tactic
expected to solve the initial goal after the extra assumptionform
is added and possibly destructed. If theas intro_pattern
clause generates more than one subgoal,tactic
is applied to all of them.

Variant
eenough form by tactic

Variant
eenough form as intro_pattern by tactic
While the different variants of
enough
expect that no existential variables are generated by the tactic,eenough
removes this constraint.

Variant
cut form
¶ This tactic applies to any goal. It implements the nondependent case of the “App” rule given in Typing rules. (This is Modus Ponens inference rule.)
cut U
transforms the current goalT
into the two following subgoals:U > T
andU
. The subgoalU > T
comes first in the list of remaining subgoal to prove.

Variant
specialize (ident term*) as intro_pattern?

Variant
specialize ident with bindings_list as intro_pattern?
¶ The tactic
specialize
works on local hypothesisident
. The premises of this hypothesis (either universal quantifications or nondependent implications) are instantiated by concrete terms coming either from argumentsterm*
or from a bindings list. In the first form the application toterm*
can be partial. The first form is equivalent toassert (ident := ident term*)
. In the second form, instantiation elements can also be partial. In this case the uninstantiated arguments are inferred by unification if possible or left quantified in the hypothesis otherwise. With theas
clause, the local hypothesisident
is left unchanged and instead, the modified hypothesis is introduced as specified by theintro_pattern
. The nameident
can also refer to a global lemma or hypothesis. In this case, for compatibility reasons, the behavior ofspecialize
is close to that ofgeneralize
: the instantiated statement becomes an additional premise of the goal. Theas
clause is especially useful in this case to immediately introduce the instantiated statement as a local hypothesis.

generalize term
¶ This tactic applies to any goal. It generalizes the conclusion with respect to some term.
Example
 Goal forall x y:nat, 0 <= x + y + y.
 1 subgoal ============================ forall x y : nat, 0 <= x + y + y
 Proof.
 intros *.
 1 subgoal x, y : nat ============================ 0 <= x + y + y
 Show.
 1 subgoal x, y : nat ============================ 0 <= x + y + y
 generalize (x + y + y).
 1 subgoal x, y : nat ============================ forall n : nat, 0 <= n
If the goal is G
and t
is a subterm of type T
in the goal,
then generalize t
replaces the goal by forall (x:T), G′
where G′
is obtained from G
by replacing all occurrences of t
by x
. The
name of the variable (here n
) is chosen based on T
.

Variant
generalize term+
This is equivalent to
generalize term; … ; generalize term
. Note that the sequence of term _{i} ‘s are processed from n to 1.

Variant
generalize term at num+
This is equivalent to
generalize term
but it generalizes only over the specified occurrences ofterm
(counting from left to right on the expression printed using optionPrinting All
).

Variant
generalize term as ident
This is equivalent to
generalize term
but it usesident
to name the generalized hypothesis.

Variant
generalize term at num+ as ident+,
This is the most general form of
generalize
that combines the previous behaviors.

Variant
generalize dependent term
This generalizes term but also all hypotheses that depend on
term
. It clears the generalized hypotheses.

evar (ident : term)
¶ The
evar
tactic creates a new local definition namedident
with typeterm
in the context. The body of this binding is a fresh existential variable.

instantiate (ident := term )
¶ The instantiate tactic refines (see
refine
) an existential variableident
with the termterm
. It is equivalent to only [ident]:refine term
(preferred alternative).Note
To be able to refer to an existential variable by name, the user must have given the name explicitly (see Existential variables).
Note
When you are referring to hypotheses which you did not name explicitly, be aware that Coq may make a different decision on how to name the variable in the current goal and in the context of the existential variable. This can lead to surprising behaviors.

Variant
instantiate (num := term)
This variant allows to refer to an existential variable which was not named by the user. The
num
argument is the position of the existential variable from right to left in the goal. Because this variant is not robust to slight changes in the goal, its use is strongly discouraged.

Variant
instantiate ( num := term ) in ( Type of ident )
These allow to refer respectively to existential variables occurring in a hypothesis or in the body or the type of a local definition.

Variant
instantiate
Without argument, the instantiate tactic tries to solve as many existential variables as possible, using information gathered from other tactics in the same tactical. This is automatically done after each complete tactic (i.e. after a dot in proof mode), but not, for example, between each tactic when they are sequenced by semicolons.

admit
¶
The admit tactic allows temporarily skipping a subgoal so as to
progress further in the rest of the proof. A proof containing admitted
goals cannot be closed with Qed
but only with Admitted
.

Variant
give_up
Synonym of
admit
.

absurd term
¶ This tactic applies to any goal. The argument term is any proposition
P
of typeProp
. This tactic applies False elimination, that is it deduces the current goal from False, and generates as subgoals∼P
andP
. It is very useful in proofs by cases, where some cases are impossible. In most cases,P
or∼P
is one of the hypotheses of the local context.

contradiction
¶ This tactic applies to any goal. The contradiction tactic attempts to find in the current context (after all intros) an hypothesis that is equivalent to an empty inductive type (e.g.
False
), to the negation of a singleton inductive type (e.g.True
orx=x
), or two contradictory hypotheses.

Error
No such assumption

contradict ident
¶ This tactic allows manipulating negated hypothesis and goals. The name
ident
should correspond to a hypothesis. Withcontradict H
, the current goal and context is transformed in the following way: H:¬A ⊢ B becomes ⊢ A
 H:¬A ⊢ ¬B becomes H: B ⊢ A
 H: A ⊢ B becomes ⊢ ¬A
 H: A ⊢ ¬B becomes H: B ⊢ ¬A

exfalso
¶ This tactic implements the “ex falso quodlibet” logical principle: an elimination of False is performed on the current goal, and the user is then required to prove that False is indeed provable in the current context. This tactic is a macro for
elimtype False
.
Case analysis and induction¶
The tactics presented in this section implement induction or case analysis on inductive or coinductive objects (see Inductive Definitions).

destruct term
¶ This tactic applies to any goal. The argument
term
must be of inductive or coinductive type and the tactic generates subgoals, one for each possible form ofterm
, i.e. one for each constructor of the inductive or coinductive type. Unlikeinduction
, no induction hypothesis is generated bydestruct
.There are special cases:
If
term
is an identifierident
denoting a quantified variable of the conclusion of the goal, thendestruct ident
behaves asintros until ident; destruct ident
. Ifident
is not anymore dependent in the goal after application ofdestruct
, it is erased (to avoid erasure, use parentheses, as indestruct (ident)
). If term is a num, then destruct num behaves asintros until num followed by destruct applied to the last introduced hypothesis.
Note
For destruction of a numeral, use syntax destruct (num) (not very interesting anyway).
In case term is an hypothesis
ident
of the context, andident
is not anymore dependent in the goal after application ofdestruct
, it is erased (to avoid erasure, use parentheses, as indestruct (ident)
).The argument
term
can also be a pattern of which holes are denoted by “_”. In this case, the tactic checks that all subterms matching the pattern in the conclusion and the hypotheses are compatible and performs case analysis using this subterm.

Variant
destruct term+,
This is a shortcut for
destruct term; …; destruct term
.

Variant
destruct term as disj_conj_intro_pattern
This behaves as
destruct term
but uses the names inintro_pattern
to name the variables introduced in the context. Theintro_pattern
must have the form[p11 … p1n  …  pm1 … pmn ]
with m being the number of constructors of the type ofterm
. Each variable introduced bydestruct
in the context of the ith goal gets its name from the listpi1 … pin
in order. If there are not enough names,destruct
invents names for the remaining variables to introduce. More generally, thepij
can be any introduction pattern (seeintros
). This provides a concise notation for chaining destruction of an hypothesis.

Variant
destruct term eqn:naming_intro_pattern
This behaves as
destruct term
but adds an equation betweenterm
and the value thatterm
takes in each of the possible cases. The name of the equation is specified bynaming_intro_pattern
(seeintros
), in particular ? can be used to let Coq generate a fresh name.

Variant
destruct term with bindings_list
This behaves like
destruct term
providing explicit instances for the dependent premises of the type ofterm
(see syntax of bindings).

Variant
edestruct term
¶ This tactic behaves like
destruct term
except that it does not fail if the instance of a dependent premises of the type ofterm
is not inferable. Instead, the unresolved instances are left as existential variables to be inferred later, in the same way aseapply
does.

Variant
destruct term using term with bindings_list
These are synonyms of
induction term using term
andinduction term using term with bindings_list
.

Variant
destruct term in goal_occurrences
This syntax is used for selecting which occurrences of
term
the case analysis has to be done on. Thein goal_occurrences
clause is an occurrence clause whose syntax and behavior is described in occurences sets.

Variant
destruct term with bindings_list as disj_conj_intro_pattern eqn:naming_intro_pattern using term with bindings_list in goal_occurrences

Variant
edestruct term with bindings_list as disj_conj_intro_pattern eqn:naming_intro_pattern using term with bindings_list in goal_occurrences
These are the general forms of
destruct
andedestruct
. They combine the effects of the with, as, eqn:, using, and in clauses.

Variant
case term
¶ The tactic
case
is a more basic tactic to perform case analysis without recursion. It behaves aselim term
but using a caseanalysis elimination principle and not a recursive one.

Variant
case term with bindings_list
Analogous to
elim term with bindings_list
above.

Variant
ecase term with bindings_list?
¶ In case the type of
term
has dependent premises, or dependent premises whose values are not inferable from thewith bindings_list
clause,ecase
turns them into existential variables to be resolved later on.

Variant
simple destruct ident
¶ This tactic behaves as
intros until ident; case ident
whenident
is a quantified variable of the goal.

Variant
simple destruct num
This tactic behaves as
intros until num; case ident
whereident
is the name given byintros until num
to thenum
th nondependent premise of the goal.

Variant
case_eq term
The tactic
case_eq
is a variant of thecase
tactic that allow to perform case analysis on a term without completely forgetting its original form. This is done by generating equalities between the original form of the term and the outcomes of the case analysis.

induction term
¶ This tactic applies to any goal. The argument
term
must be of inductive type and the tacticinduction
generates subgoals, one for each possible form ofterm
, i.e. one for each constructor of the inductive type.If the argument is dependent in either the conclusion or some hypotheses of the goal, the argument is replaced by the appropriate constructor form in each of the resulting subgoals and induction hypotheses are added to the local context using names whose prefix is IH.
There are particular cases:
If term is an identifier
ident
denoting a quantified variable of the conclusion of the goal, then inductionident behaves asintros until ident; induction ident
. Ifident
is not anymore dependent in the goal after application ofinduction
, it is erased (to avoid erasure, use parentheses, as ininduction (ident)
).If
term
is anum
, theninduction num
behaves asintros until num
followed byinduction
applied to the last introduced hypothesis.Note
For simple induction on a numeral, use syntax induction (num) (not very interesting anyway).
In case term is an hypothesis
ident
of the context, andident
is not anymore dependent in the goal after application ofinduction
, it is erased (to avoid erasure, use parentheses, as ininduction (ident)
).The argument
term
can also be a pattern of which holes are denoted by “_”. In this case, the tactic checks that all subterms matching the pattern in the conclusion and the hypotheses are compatible and performs induction using this subterm.
Example
 Lemma induction_test : forall n:nat, n = n > n <= n.
 1 subgoal ============================ forall n : nat, n = n > n <= n
 intros n H.
 1 subgoal n : nat H : n = n ============================ n <= n
 induction n.
 2 subgoals H : 0 = 0 ============================ 0 <= 0 subgoal 2 is: S n <= S n

Error
Not an inductive product

Error
Unable to find an instance for the variables ident … ident
Use in this case the variant
elim ... with
below.

Variant
induction term as disj_conj_intro_pattern
This behaves as
induction
but uses the names indisj_conj_intro_pattern
to name the variables introduced in the context. Thedisj_conj_intro_pattern
must typically be of the form[ p
_{11}… p
_{1n} …  p
_{m1}… p
_{mn}]
withm
being the number of constructors of the type ofterm
. Each variable introduced by induction in the context of the ith goal gets its name from the listp
_{i1}… p
_{in} in order. If there are not enough names, induction invents names for the remaining variables to introduce. More generally, thep
_{ij} can be any disjunctive/conjunctive introduction pattern (seeintros ...
). For instance, for an inductive type with one constructor, the pattern notation(p
_{1}, … , p
_{n})
can be used instead of[ p
_{1}… p
_{n}]
.

Variant
induction term with bindings_list
This behaves like
induction
providing explicit instances for the premises of the type ofterm
(see bindings list).

Variant
einduction term
¶ This tactic behaves like
induction
except that it does not fail if some dependent premise of the type ofterm
is not inferable. Instead, the unresolved premises are posed as existential variables to be inferred later, in the same way aseapply
does.

Variant
induction term using term
¶ This behaves as
induction
but usingterm
as induction scheme. It does not expect the conclusion of the type of the firstterm
to be inductive.

Variant
induction term using term with bindings_list
This behaves as
induction ... using ...
but also providing instances for the premises of the type of the secondterm
.

Variant
induction term+, using qualid
This syntax is used for the case
qualid
denotes an induction principle with complex predicates as the induction principles generated byFunction
orFunctional Scheme
may be.

Variant
induction term in goal_occurrences
This syntax is used for selecting which occurrences of
term
the induction has to be carried on. Thein goal_occurrences
clause is an occurrence clause whose syntax and behavior is described in occurences sets. If variables or hypotheses not mentioningterm
in their type are listed ingoal_occurrences
, those are generalized as well in the statement to prove.Example
 Lemma comm x y : x + y = y + x.
 1 subgoal x, y : nat ============================ x + y = y + x
 induction y in x  *.
 2 subgoals x : nat ============================ x + 0 = 0 + x subgoal 2 is: x + S y = S y + x
 Show 2.
 subgoal 2 is: x, y : nat IHy : forall x : nat, x + y = y + x ============================ x + S y = S y + x

Variant
induction term with bindings_list as disj_conj_intro_pattern using term with bindings_list in goal_occurrences

Variant
einduction term with bindings_list as disj_conj_intro_pattern using term with bindings_list in goal_occurrences
These are the most general forms of
induction
andeinduction
. It combines the effects of the with, as, using, and in clauses.

Variant
elim term
¶ This is a more basic induction tactic. Again, the type of the argument
term
must be an inductive type. Then, according to the type of the goal, the tacticelim
chooses the appropriate destructor and applies it as the tacticapply
would do. For instance, if the proof context containsn:nat
and the current goal isT
of typeProp
, thenelim n
is equivalent toapply nat_ind with (n:=n)
. The tacticelim
does not modify the context of the goal, neither introduces the induction loading into the context of hypotheses. More generally,elim term
also works when the type ofterm
is a statement with premises and whose conclusion is inductive. In that case the tactic performs induction on the conclusion of the type ofterm
and leaves the nondependent premises of the type as subgoals. In the case of dependent products, the tactic tries to find an instance for which the elimination lemma applies and fails otherwise.

Variant
elim term with bindings_list
¶ Allows to give explicit instances to the premises of the type of
term
(see bindings list).

Variant
eelim term
¶ In case the type of
term
has dependent premises, this turns them into existential variables to be resolved later on.

Variant
elim term using term with bindings_list
Allows the user to give explicitly an induction principle
term
that is not the standard one for the underlying inductive type ofterm
. Thebindings_list
clause allows instantiating premises of the type ofterm
.

Variant
elim term with bindings_list using term with bindings_list

Variant
eelim term with bindings_list using term with bindings_list
These are the most general forms of
elim
andeelim
. It combines the effects of theusing
clause and of the two uses of thewith
clause.

Variant
elimtype form
¶ The argument
form
must be inductively defined.elimtype I
is equivalent tocut I. intro Hn; elim Hn; clear Hn.
Therefore the hypothesisHn
will not appear in the context(s) of the subgoal(s). Conversely, ift
is aterm
of (inductive) typeI
that does not occur in the goal, thenelim t
is equivalent toelimtype I; 2:exact t.

Variant
simple induction ident
¶ This tactic behaves as
intros until ident; elim ident
whenident
is a quantified variable of the goal.

Variant
simple induction num
This tactic behaves as
intros until num; elim ident
whereident
is the name given byintros until num
to thenum
th nondependent premise of the goal.

double induction ident ident
¶ This tactic is deprecated and should be replaced by
induction ident; induction ident
(orinduction ident ; destruct ident
depending on the exact needs).

Variant
double induction num1 num2
This tactic is deprecated and should be replaced by
induction num1; induction num3
wherenum3
is the result ofnum2  num1

dependent induction ident
¶ The experimental tactic dependent induction performs induction inversion on an instantiated inductive predicate. One needs to first require the Coq.Program.Equality module to use this tactic. The tactic is based on the BasicElim tactic by Conor McBride [McB00] and the work of Cristina Cornes around inversion [CT95]. From an instantiated inductive predicate and a goal, it generates an equivalent goal where the hypothesis has been generalized over its indexes which are then constrained by equalities to be the right instances. This permits to state lemmas without resorting to manually adding these equalities and still get enough information in the proofs.
Example
 Lemma le_minus : forall n:nat, n < 1 > n = 0.
 1 subgoal ============================ forall n : nat, n < 1 > n = 0
 intros n H ; induction H.
 2 subgoals n : nat ============================ n = 0 subgoal 2 is: n = 0
Here we did not get any information on the indexes to help fulfill
this proof. The problem is that, when we use the induction
tactic, we
lose information on the hypothesis instance, notably that the second
argument is 1 here. Dependent induction solves this problem by adding
the corresponding equality to the context.
 Require Import Coq.Program.Equality.
 Lemma le_minus : forall n:nat, n < 1 > n = 0.
 1 subgoal ============================ forall n : nat, n < 1 > n = 0
 intros n H ; dependent induction H.
 2 subgoals ============================ 0 = 0 subgoal 2 is: n = 0
The subgoal is cleaned up as the tactic tries to automatically simplify the subgoals with respect to the generated equalities. In this enriched context, it becomes possible to solve this subgoal.
 reflexivity.
 1 subgoal n : nat H : S n <= 0 IHle : 0 = 1 > n = 0 ============================ n = 0
Now we are in a contradictory context and the proof can be solved.
 inversion H.
 No more subgoals.
This technique works with any inductive predicate. In fact, the
dependent induction
tactic is just a wrapper around the induction
tactic. One can make its own variant by just writing a new tactic
based on the definition found in Coq.Program.Equality
.

Variant
dependent induction ident generalizing ident+
This performs dependent induction on the hypothesis
ident
but first generalizes the goal by the given variables so that they are universally quantified in the goal. This is generally what one wants to do with the variables that are inside some constructors in the induction hypothesis. The other ones need not be further generalized.

Variant
dependent destruction ident
¶ This performs the generalization of the instance
ident
but usesdestruct
instead of induction on the generalized hypothesis. This gives results equivalent toinversion
ordependent inversion
if the hypothesis is dependent.
See also the larger example of dependent induction
and an explanation of the underlying technique.

function induction (qualid term+)
¶ The tactic functional induction performs case analysis and induction following the definition of a function. It makes use of a principle generated by
Function
(see Advanced recursive functions) orFunctional Scheme
(see Generation of induction principles with Functional Scheme). Note that this tactic is only available after a
Example
 Require Import FunInd.
 [Loading ML file extraction_plugin.cmxs … done] [Loading ML file recdef_plugin.cmxs … done]
 Functional Scheme minus_ind := Induction for minus Sort Prop.
 sub_equation is defined minus_ind is defined
 Check minus_ind.
 minus_ind : forall P : nat > nat > nat > Prop, (forall n m : nat, n = 0 > P 0 m n) > (forall n m k : nat, n = S k > m = 0 > P (S k) 0 n) > (forall n m k : nat, n = S k > forall l : nat, m = S l > P k l (k  l) > P (S k) (S l) (k  l)) > forall n m : nat, P n m (n  m)
 Lemma le_minus (n m:nat) : n  m <= n.
 1 subgoal n, m : nat ============================ n  m <= n
 functional induction (minus n m) using minus_ind; simpl; auto.
 No more subgoals.
 Qed.
 le_minus is defined
Note
(qualid term+)
must be a correct full application
of qualid
. In particular, the rules for implicit arguments are the
same as usual. For example use qualid
if you want to write implicit
arguments explicitly.
Note
functional induction (f x1 x2 x3)
is actually a wrapper for
induction x1, x2, x3, (f x1 x2 x3) using qualid
followed by a cleaning
phase, where qualid
is the induction principle registered for f
(by the Function
(see Advanced recursive functions) or
Functional Scheme
(see Generation of induction principles with Functional Scheme)
command) corresponding to the sort of the goal. Therefore
functional induction
may fail if the induction scheme qualid
is not
defined. See also Advanced recursive functions for the function
terms accepted by Function
.
Note
There is a difference between obtaining an induction scheme
for a function by using Function
(see Advanced recursive functions)
and by using Functional Scheme
after a normal definition using
Fixpoint
or Definition
. See Advanced recursive functions
for details.
 See also: Advanced recursive functions
 Generation of induction principles with Functional Scheme
inversion

Error
Not the right number of induction arguments
¶

Variant
functional induction (qualid term+) as disj_conj_intro_pattern using term with bindings_list
Similarly to
induction
andelim
, this allows giving explicitly the name of the introduced variables, the induction principle, and the values of dependent premises of the elimination scheme, including predicates for mutual induction whenqualid
is part of a mutually recursive definition.

discriminate term
¶ This tactic proves any goal from an assumption stating that two structurally different
terms
of an inductive set are equal. For example, from(S (S O))=(S O)
we can derive by absurdity any proposition.The argument
term
is assumed to be a proof of a statement of conclusionterm = term
with the two terms being elements of an inductive set. To build the proof, the tactic traverses the normal forms [3] of the terms looking for a couple of subtermsu
andw
(u
subterm of the normal form ofterm
andw
subterm of the normal form ofterm
), placed at the same positions and whose head symbols are two different constructors. If such a couple of subterms exists, then the proof of the current goal is completed, otherwise the tactic fails.
Note
The syntax discriminate ident
can be used to refer to a hypothesis
quantified in the goal. In this case, the quantified hypothesis whose name is
ident
is first introduced in the local context using
intros until ident
.

Error
No primitive equality found
¶

Error
Not a discriminable equality
¶

Variant
discriminate num
This does the same thing as
intros until num
followed bydiscriminate ident
whereident
is the identifier for the last introduced hypothesis.

Variant
discriminate term with bindings_list
This does the same thing as
discriminate term
but using the given bindings to instantiate parameters or hypotheses ofterm
.

Variant
ediscriminate num

Variant
ediscriminate term with bindings_list?
¶ This works the same as
discriminate
but if the type ofterm
, or the type of the hypothesis referred to bynum
, has uninstantiated parameters, these parameters are left as existential variables.

Variant
discriminate
This behaves like
discriminate ident
if ident is the name of an hypothesis to whichdiscriminate
is applicable; if the current goal is of the formterm <> term
, this behaves asintro ident; discriminate ident
.
Error
No discriminable equalities
¶

Error

injection term
¶ The injection tactic exploits the property that constructors of inductive types are injective, i.e. that if
c
is a constructor of an inductive type andc t
_{1} andc t
_{2} are equal thent
_{1} andt
_{2} are equal too.If
term
is a proof of a statement of conclusionterm = term
, theninjection
applies the injectivity of constructors as deep as possible to derive the equality of all the subterms ofterm
andterm
at positions where the terms start to differ. For example, from(S p, S n) = (q, S (S m))
we may deriveS p = q
andn = S m
. For this tactic to work, the terms should be typed with an inductive type and they should be neither convertible, nor having a different head constructor. If these conditions are satisfied, the tactic derives the equality of all the subterms at positions where they differ and adds them as antecedents to the conclusion of the current goal.
Example
Consider the following goal:
 Inductive list : Set :=  nil : list  cons : nat > list > list.
 list is defined list_rect is defined list_ind is defined list_rec is defined
 Variable P : list > Prop.
 Toplevel input, characters 026: > Variable P : list > Prop. > ^^^^^^^^^^^^^^^^^^^^^^^^^^ Warning: P is declared as a local axiom [localdeclaration,scope] P is declared
 Goal forall l n, P nil > cons n l = cons 0 nil > P l.
 1 subgoal ============================ forall (l : list) (n : nat), P nil > cons n l = cons 0 nil > P l
 intros.
 1 subgoal l : list n : nat H : P nil H0 : cons n l = cons 0 nil ============================ P l
 injection H0.
 1 subgoal l : list n : nat H : P nil H0 : cons n l = cons 0 nil ============================ l = nil > n = 0 > P l
Beware that injection yields an equality in a sigma type whenever the
injected object has a dependent type P
with its two instances in
different types (P t
_{1} … t
_{n} )
and
(P u
_{1} … u
_{n} _{)}. If t
_{1} and
u
_{1} are the same and have for type an inductive type for which a decidable
equality has been declared using the command Scheme Equality
(see Generation of induction principles with Scheme),
the use of a sigma type is avoided.
Note
If some quantified hypothesis of the goal is named ident
,
then injection ident
first introduces the hypothesis in the local
context using intros until ident
.

Error
Not a projectable equality but a discriminable one
¶

Error
Nothing to do, it is an equality between convertible terms
¶

Error
Not a primitive equality
¶

Error
Nothing to inject
¶

Variant
injection num
This does the same thing as
intros until num
followed byinjection ident
whereident
is the identifier for the last introduced hypothesis.

Variant
injection term with bindings_list
This does the same as
injection term
but using the given bindings to instantiate parameters or hypotheses ofterm
.

Variant
einjection num

Variant
einjection term with bindings_list?
¶ This works the same as
injection
but if the type ofterm
, or the type of the hypothesis referred to bynum
, has uninstantiated parameters, these parameters are left as existential variables.

Variant
injection
If the current goal is of the form
term <> term
, this behaves asintro ident; injection ident
.
Error
goal does not satisfy the expected preconditions
¶

Error

Variant
injection term with bindings_list? as intro_pattern+

Variant
injection num as intro_pattern+

Variant
injection as intro_pattern+

Variant
einjection term with bindings_list? as intro_pattern+

Variant
einjection num as intro_pattern+

Variant
einjection as intro_pattern+
These variants apply
intros intro_pattern+
after the call toinjection
oreinjection
so that all equalities generated are moved in the context of hypotheses. The number ofintro_pattern
must not exceed the number of equalities newly generated. If it is smaller, fresh names are automatically generated to adjust the list ofintro_pattern
to the number of new equalities. The original equality is erased if it corresponds to an hypothesis.

Option
Structural Injection
¶ This option ensure that
injection term
erases the original hypothesis and leaves the generated equalities in the context rather than putting them as antecedents of the current goal, as if givinginjection term as
(with an empty list of names). This option is off by default.

Option
Keep Proof Equalities
¶ By default,
injection
only creates new equalities betweenterms
whose type is in sortType
orSet
, thus implementing a special behavior for objects that are proofs of a statement inProp
. This option controls this behavior.

inversion ident
¶ Let the type of
ident
in the local context be(I t)
, whereI
is a (co)inductive predicate. Then,inversion
applied toident
derives for each possible constructorc i
of(I t)
, all the necessary conditions that should hold for the instance(I t)
to be proved byc i
.
Note
If ident
does not denote a hypothesis in the local context but
refers to a hypothesis quantified in the goal, then the latter is
first introduced in the local context using intros until ident
.
Note
As inversion
proofs may be large in size, we recommend the
user to stock the lemmas whenever the same instance needs to be
inverted several times. See Generation of inversion principles with Derive Inversion.
Note
Part of the behavior of the inversion
tactic is to generate
equalities between expressions that appeared in the hypothesis that is
being processed. By default, no equalities are generated if they
relate two proofs (i.e. equalities between terms
whose type is in sort
Prop
). This behavior can be turned off by using the option
:opt`Keep Proof Equalities`.

Variant
inversion num
This does the same thing as
intros until num
theninversion ident
whereident
is the identifier for the last introduced hypothesis.

Variant
inversion ident as intro_pattern
This generally behaves as inversion but using names in
intro_pattern
for naming hypotheses. Theintro_pattern
must have the form[p
_{11}… p
_{1n} …  p
_{m1}… p
_{mn}]
with m being the number of constructors of the type ofident
. Be careful that the list must be of length m even ifinversion
discards some cases (which is precisely one of its roles): for the discarded cases, just use an empty list (i.e. n = 0).The arguments of the ith constructor and the equalities thatinversion
introduces in the context of the goal corresponding to the ith constructor, if it exists, get their names from the listp
_{i1}… p
_{in} in order. If there are not enough names,inversion
invents names for the remaining variables to introduce. In case an equation splits into several equations (becauseinversion
appliesinjection
on the equalities it generates), the corresponding namep
_{ij} in the list must be replaced by a sublist of the form[p
_{ij1}… p
_{ijq}]
(or, equivalently,(p
_{ij1}, …, p
_{ijq})
) where q is the number of subequalities obtained from splitting the original equation. Here is an example. Theinversion ... as
variant ofinversion
generally behaves in a slightly more expectable way thaninversion
(no artificial duplication of some hypotheses referring to other hypotheses). To take benefit of these improvements, it is enough to useinversion ... as []
, letting the names being finally chosen by Coq.Example
 Inductive contains0 : list nat > Prop :=  in_hd : forall l, contains0 (0 :: l)  in_tl : forall l b, contains0 l > contains0 (b :: l).
 contains0 is defined contains0_ind is defined
 Goal forall l:list nat, contains0 (1 :: l) > contains0 l.
 1 subgoal ============================ forall l : list nat, contains0 (1 :: l) > contains0 l
 intros l H; inversion H as [  l’ p Hl’ [Heqp Heql’] ].
 1 subgoal l : list nat H : contains0 (1 :: l) l’ : list nat p : nat Hl’ : contains0 l Heqp : p = 1 Heql’ : l’ = l ============================ contains0 l

Variant
inversion num as intro_pattern
This allows naming the hypotheses introduced by
inversion num
in the context.

Variant
inversion_clear ident as intro_pattern
This allows naming the hypotheses introduced by
inversion_clear
in the context. Notice that hypothesis names can be provided as ifinversion
were called, even though theinversion_clear
will eventually erase the hypotheses.

Variant
inversion ident in ident+
Let
ident+
be identifiers in the local context. This tactic behaves as generalizingident+
, and then performinginversion
.

Variant
inversion ident as intro_pattern in ident+
This allows naming the hypotheses introduced in the context by
inversion ident in ident+
.

Variant
inversion_clear ident in ident+
Let
ident+
be identifiers in the local context. This tactic behaves as generalizingident+
, and then performinginversion_clear
.

Variant
inversion_clear ident as intro_pattern in ident+
This allows naming the hypotheses introduced in the context by
inversion_clear ident in ident+
.

Variant
dependent inversion ident
¶ That must be used when
ident
appears in the current goal. It acts likeinversion
and then substitutesident
for the corresponding@term
in the goal.

Variant
dependent inversion ident as intro_pattern
This allows naming the hypotheses introduced in the context by
dependent inversion ident
.

Variant
dependent inversion_clear ident
Like
dependent inversion
, except thatident
is cleared from the local context.

Variant
dependent inversion_clear ident as intro_pattern
This allows naming the hypotheses introduced in the context by
dependent inversion_clear ident
.

Variant
dependent inversion ident with term
This variant allows you to specify the generalization of the goal. It is useful when the system fails to generalize the goal automatically. If
ident
has type(I t)
andI
has type \(\forall\)(x:T), s
, thenterm
must be of typeI:
\(\forall\)(x:T), I x > s’
wheres’
is the type of the goal.

Variant
dependent inversion ident as intro_pattern with term
This allows naming the hypotheses introduced in the context by
dependent inversion ident with term
.

Variant
dependent inversion_clear ident with term
Like
dependent inversion ...
with but clearsident
from the local context.

Variant
dependent inversion_clear ident as intro_pattern with term
This allows naming the hypotheses introduced in the context by
dependent inversion_clear ident with term
.

Variant
simple inversion ident
¶ It is a very primitive inversion tactic that derives all the necessary equalities but it does not simplify the constraints as
inversion
does.

Variant
simple inversion ident as intro_pattern
This allows naming the hypotheses introduced in the context by
simple inversion
.

Variant
inversion ident using ident
Let
ident
have type(I t)
(I
an inductive predicate) in the local context, andident
be a (dependent) inversion lemma. Then, this tactic refines the current goal with the specified lemma.

Variant
inversion ident using ident in ident+
This tactic behaves as generalizing
ident+
, then doinginversion ident using ident
.

Variant
inversion_sigma
This tactic turns equalities of dependent pairs (e.g.,
existT P x p = existT P y q
, frequently left over by inversion on a dependent type family) into pairs of equalities (e.g., a hypothesisH : x = y
and a hypothesis of typerew H in p = q
); these hypotheses can subsequently be simplified usingsubst
, without ever invoking any kind of axiom asserting uniqueness of identity proofs. If you want to explicitly specify the hypothesis to be inverted, or name the generated hypotheses, you can invokeinduction H as [H1 H2] using eq_sigT_rect.
This tactic also works forsig
,sigT2
, andsig2
, and there are similareq_sig
***_rect
induction lemmas.
Example
Nondependent inversion.
Let us consider the relation Le over natural numbers and the following variables:
 Inductive Le : nat > nat > Set :=  LeO : forall n:nat, Le 0 n  LeS : forall n m:nat, Le n m > Le (S n) (S m).
 Le is defined Le_rect is defined Le_ind is defined Le_rec is defined
 Variable P : nat > nat > Prop.
 Toplevel input, characters 032: > Variable P : nat > nat > Prop. > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Warning: P is declared as a local axiom [localdeclaration,scope] P is declared
 Variable Q : forall n m:nat, Le n m > Prop.
 Toplevel input, characters 044: > Variable Q : forall n m:nat, Le n m > Prop. > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Warning: Q is declared as a local axiom [localdeclaration,scope] Q is declared
Let us consider the following goal:
 Goal forall n m, Le (S n) m > P n m.
 Le is defined Le_rect is defined Le_ind is defined Le_rec is defined Toplevel input, characters 78–46: Warning: P is declared as a local axiom [localdeclaration,scope] P is declared Toplevel input, characters 45–1: Warning: Q is declared as a local axiom [localdeclaration,scope] Q is declared 1 subgoal ============================ forall n m : nat, Le (S n) m > P n m
 intros.
 1 subgoal n, m : nat H : Le (S n) m ============================ P n m
 Show.
 1 subgoal n, m : nat H : Le (S n) m ============================ P n m
To prove the goal, we may need to reason by cases on H and to derive that m is necessarily of the form (S m 0 ) for certain m 0 and that (Le n m 0 ). Deriving these conditions corresponds to prove that the only possible constructor of (Le (S n) m) isLeS and that we can invert the> in the type of LeS. This inversion is possible because Le is the smallest set closed by the constructors LeO and LeS.
 inversion_clear H.
 1 subgoal n, m, m0 : nat H0 : Le n m0 ============================ P n (S m0)
Note that m has been substituted in the goal for (S m0) and that the hypothesis (Le n m0) has been added to the context.
Sometimes it is interesting to have the equality m=(S m0) in the context to use it after. In that case we can use inversion that does not clear the equalities:
 inversion H.
 1 subgoal n, m : nat H : Le (S n) m n0, m0 : nat H1 : Le n m0 H0 : n0 = n H2 : S m0 = m ============================ P n (S m0)
Example
Dependent inversion.
Let us consider the following goal:
 Inductive Le : nat > nat > Set :=  LeO : forall n:nat, Le 0 n  LeS : forall n m:nat, Le n m > Le (S n) (S m).
 Le is defined Le_rect is defined Le_ind is defined Le_rec is defined
 Variable P : nat > nat > Prop.
 Toplevel input, characters 032: > Variable P : nat > nat > Prop. > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Warning: P is declared as a local axiom [localdeclaration,scope] P is declared
 Variable Q : forall n m:nat, Le n m > Prop.
 Toplevel input, characters 044: > Variable Q : forall n m:nat, Le n m > Prop. > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Warning: Q is declared as a local axiom [localdeclaration,scope] Q is declared
 Goal forall n m (H:Le (S n) m), Q (S n) m H.
 1 subgoal ============================ forall (n m : nat) (H : Le (S n) m), Q (S n) m H
 intros.
 1 subgoal n, m : nat H : Le (S n) m ============================ Q (S n) m H
 Show.
 1 subgoal n, m : nat H : Le (S n) m ============================ Q (S n) m H
As H occurs in the goal, we may want to reason by cases on its structure and so, we would like inversion tactics to substitute H by the corresponding @term in constructor form. Neither Inversion nor Inversion_clear make such a substitution. To have such a behavior we use the dependent inversion tactics:
 dependent inversion_clear H.
 1 subgoal n, m, m0 : nat l : Le n m0 ============================ Q (S n) (S m0) (LeS n m0 l)
Note that H has been substituted by (LeS n m0 l) andm by (S m0).
Example
Using inversion_sigma.
Let us consider the following inductive type of lengthindexed lists, and a lemma about inverting equality of cons:
 Require Import Coq.Logic.Eqdep_dec.
 Inductive vec A : nat > Type :=  nil : vec A O  cons {n} (x : A) (xs : vec A n) : vec A (S n).
 vec is defined vec_rect is defined vec_ind is defined vec_rec is defined
 Lemma invert_cons : forall A n x xs y ys, @cons A n x xs = @cons A n y ys > xs = ys.
 1 subgoal ============================ forall (A : Type) (n : nat) (x : A) (xs : vec A n) (y : A) (ys : vec A n), cons A x xs = cons A y ys > xs = ys
 Proof.
 intros A n x xs y ys H.
 1 subgoal A : Type n : nat x : A xs : vec A n y : A ys : vec A n H : cons A x xs = cons A y ys ============================ xs = ys
After performing inversion, we are left with an equality of existTs:
 inversion H.
 1 subgoal A : Type n : nat x : A xs : vec A n y : A ys : vec A n H : cons A x xs = cons A y ys H1 : x = y H2 : existT (fun n : nat => vec A n) n xs = existT (fun n : nat => vec A n) n ys ============================ xs = ys
We can turn this equality into a usable form with inversion_sigma:
 inversion_sigma.
 1 subgoal A : Type n : nat x : A xs : vec A n y : A ys : vec A n H : cons A x xs = cons A y ys H1 : x = y H0 : n = n H3 : eq_rect n (fun a : nat => vec A a) xs n H0 = ys ============================ xs = ys
To finish cleaning up the proof, we will need to use the fact that that all proofs of n = n for n a nat are eq_refl:
 let H := match goal with H : n = n  _ => H end in pose proof (Eqdep_dec.UIP_refl_nat _ H); subst H.
 1 subgoal A : Type n : nat x : A xs : vec A n y : A ys : vec A n H : cons A x xs = cons A y ys H1 : x = y H3 : eq_rect n (fun a : nat => vec A a) xs n eq_refl = ys ============================ xs = ys
 simpl in *.
 1 subgoal A : Type n : nat x : A xs : vec A n y : A ys : vec A n H : cons A x xs = cons A y ys H1 : x = y H3 : xs = ys ============================ xs = ys
Finally, we can finish the proof:
 assumption.
 No more subgoals.
 Qed.
 invert_cons is defined

fix ident num
¶ This tactic is a primitive tactic to start a proof by induction. In general, it is easier to rely on higherlevel induction tactics such as the ones described in
induction
.In the syntax of the tactic, the identifier
ident
is the name given to the induction hypothesis. The natural numbernum
tells on which premise of the current goal the induction acts, starting from 1, counting both dependent and non dependent products, but skipping local definitions. Especially, the current lemma must be composed of at leastnum
products.Like in a fix expression, the induction hypotheses have to be used on structurally smaller arguments. The verification that inductive proof arguments are correct is done only at the time of registering the lemma in the environment. To know if the use of induction hypotheses is correct at some time of the interactive development of a proof, use the command
Guarded
(see Section Requesting information).

Variant
fix ident num with (ident binder+ [{struct ident}] : type)+
This starts a proof by mutual induction. The statements to be simultaneously proved are respectively
forall binder … binder, type
. The identifiersident
are the names of the induction hypotheses. The identifiersident
are the respective names of the premises on which the induction is performed in the statements to be simultaneously proved (if not given, the system tries to guess itself what they are).

cofix ident
¶ This tactic starts a proof by coinduction. The identifier
ident
is the name given to the coinduction hypothesis. Like in a cofix expression, the use of induction hypotheses have to guarded by a constructor. The verification that the use of coinductive hypotheses is correct is done only at the time of registering the lemma in the environment. To know if the use of coinduction hypotheses is correct at some time of the interactive development of a proof, use the commandGuarded
(see Section Requesting information).
Rewriting expressions¶
These tactics use the equality eq:forall A:Type, A>A>Prop
defined in
file Logic.v
(see Logic). The notation for eq T t u
is
simply t=u
dropping the implicit type of t
and u
.
This tactic applies to any goal. The type of term
must have the form
forall (x
_{1} :A
_{1} ) ... (x
_{n} :A
_{n} ). eq term
_{1} term
_{2} .
where eq
is the Leibniz equality or a registered setoid equality.
Then rewrite term
finds the first subterm matching term_{1} in the goal,
resulting in instances term_{1}’ and term_{2}’ and then
replaces every occurrence of term_{1}’ by term_{2}’.
Hence, some of the variables x
_{i} are solved by unification,
and some of the types A
_{1}, …, A
_{n} become new
subgoals.

Error
Tactic generated a subgoal identical to the original goal. This happens if term does not occur in the goal.
¶

Variant
rewrite term in clause
Analogous to
rewrite term
but rewriting is done following clause (similarly to performing computations). For instance:rewrite H in H
_{1} will rewrite H in the hypothesis H_{1} instead of the current goal.rewrite H in H
_{1}at 1, H
_{2}at  2  *
meansrewrite H; rewrite H in H
_{1}at 1; rewrite H in H
_{2}at  2.
In particular a failure will happen if any of these three simpler tactics fails.rewrite H in * 
will dorewrite H in H
_{i} for all hypothesesH
_{i}<> H
. A success will happen as soon as at least one of these simpler tactics succeeds.rewrite H in *
is a combination ofrewrite H
andrewrite H in * 
that succeeds if at least one of these two tactics succeeds.
Orientation
>
or<
can be inserted before theterm
to rewrite.

Variant
rewrite term at occurrences
Rewrite only the given occurrences of
term
. Occurrences are specified from left to right as for pattern (pattern
). The rewrite is always performed using setoid rewriting, even for Leibniz’s equality, so one has toImport Setoid
to use this variant.

Variant
rewrite term by tactic
Use tactic to completely solve the sideconditions arising from the
rewrite
.

Variant
rewrite term+
Is equivalent to the n successive tactics
rewrite term+
, each one working on the first subgoal generated by the previous one. Orientation>
or<
can be inserted before eachterm
to rewrite. One unique clause can be added at the end after the keyword in; it will then affect all rewrite operations.In all forms of rewrite described above, a
term
to rewrite can be immediately prefixed by one of the following modifiers: ? : the tactic rewrite
?term
performs the rewrite ofterm
as many times as possible (perhaps zero time). This form never fails.  n? : works similarly, except that it will do at most n rewrites.
 ! : works as ?, except that at least one rewrite should succeed, otherwise the tactic fails.
 n! (or simply n) : precisely n rewrites of
term
will be done, leading to failure if these n rewrites are not possible.
 ? : the tactic rewrite

Variant
erewrite term

Variant
:name: erewrite
This tactic works as
rewrite term
but turning unresolved bindings into existential variables, if any, instead of failing. It has the same variants asrewrite
has.

replace term with term
¶ This tactic applies to any goal. It replaces all free occurrences of
term
in the current goal withterm
and generates the equalityterm = term
as a subgoal. This equality is automatically solved if it occurs among the assumption, or if its symmetric form occurs. It is equivalent tocut term = term; [intro H
_{n}; rewrite < H
_{n}; clear H
_{n} assumption  symmetry; try assumption]
.

Error
terms do not have convertible types
¶

Variant
replace term with term by tactic
This acts as
replace term
withterm
but applies tactic to solve the generated subgoalterm = term
.

Variant
replace term
Replaces
term
withterm’
using the first assumption whose type has the formterm = term’
orterm’ = term
.

Variant
replace > term
Replaces
term
withterm’
using the first assumption whose type has the formterm = term’

Variant
replace < term
Replaces
term
withterm’
using the first assumption whose type has the formterm’ = term

Variant
replace < term in clause
Acts as before but the replacements take place inclause (see Performing computations) and not only in the conclusion of the goal. The clause argument must not contain any type of nor value of.

Variant
cutrewrite < (term = term)

Variant
:cutrewrite:
This tactic is deprecated. It acts like
replace term with term
, or, equivalently asenough (term = term) as <
.

Variant
cutrewrite > (term = term)
This tactic is deprecated. It can be replaced by enough
(term = term) as >
.
This tactic applies to a goal that has ident
in its context and (at
least) one hypothesis, say H
, of type ident = t
or t = ident
with ident
not occurring in t
. Then it replaces ident
by
t
everywhere in the goal (in the hypotheses and in the conclusion) and
clears ident
and H
from the context.
If ident
is a local definition of the form ident := t
, it is also
unfolded and cleared.
Note
If H is itself dependent in the goal, it is replaced by the proof of reflexivity of equality.

Variant
subst
This applies subst repeatedly from top to bottom to all identifiers of the context for which an equality of the form
ident = t
ort = ident
orident := t
exists, withident
not occurring in t.
Option
Regular Subst Tactic
¶ This option controls the behavior of
subst
. When it is activated,subst
also deals with the following corner cases: A context with ordered hypotheses
ident
_{1}= ident
_{2} andident
_{1}= t
, ort′ = ident
_{1`} with t′ not a variable, and no other hypotheses of the formident
_{2}= u
oru = ident
_{2}; without the option, a second call to subst would be necessary to replaceident
_{2} by t or t′ respectively.  The presence of a recursive equation which without the option would
be a cause of failure of
subst
.  A context with cyclic dependencies as with hypotheses
ident
_{1}= f ident
_{2} andident
_{2}= g ident
_{1} which without the option would be a cause of failure ofsubst
.
Additionally, it prevents a local definition such as
ident := t
to be unfolded which otherwise it would exceptionally unfold in configurations containing hypotheses of the formident = u
, oru′ = ident
with u′ not a variable. Finally, it preserves the initial order of hypotheses, which without the option it may break. The option is on by default. A context with ordered hypotheses

Option
This tactic is for chaining rewriting steps. It assumes a goal of the
form R term term
where R is a binary relation and relies on a
database of lemmas of the form forall x y z, R x y > eq x z > R z y
where eq is typically a setoid equality. The application of stepl term
then replaces the goal by R term term
and adds a new goal stating
eq term term
.
The tactic is especially useful for parametric setoids which are not accepted
as regular setoids for rewrite
and setoid_replace
(see
Generalized rewriting).

Variant
stepr term stepr term by tactic
¶ This behaves as
stepl
but on the righthandside of the binary relation. Lemmas are expected to be of the formforall x y z, R x y > eq y z > R x z
.

change term
¶ This tactic applies to any goal. It implements the rule
Conv
given in Subtyping rules.change U
replaces the current goal T with U providing that U is wellformed and that T and U are convertible.

Error
Not convertible
¶

Variant
change term with term
This replaces the occurrences of
term
byterm
in the current goal. The termterm
andterm
must be convertible.

Variant
change term at num+ with term
This replaces the occurrences numbered
num+
ofterm by term
in the current goal. The termsterm
andterm
must be convertible.

Error
Too few occurrences
¶

Variant
change term at num+ with term in ident
This applies the change tactic not to the goal but to the hypothesis
ident
.
See also: Performing computations
Performing computations¶
This set of tactics implements different specialized usages of the
tactic change
.
All conversion tactics (including change
) can be parameterized by the
parts of the goal where the conversion can occur. This is done using
goal clauses which consists in a list of hypotheses and, optionally,
of a reference to the conclusion of the goal. For defined hypothesis
it is possible to specify if the conversion should occur on the type
part, the body part or both (default).
Goal clauses are written after a conversion tactic (tactics set
,
rewrite
, replace
and autorewrite
also use goal
clauses) and are introduced by the keyword in. If no goal clause is
provided, the default is to perform the conversion only in the
conclusion.
The syntax and description of the various goal clauses is the following:
in ident+ 
only in hypothesesident+
in ident+  *
in hypothesesident+
and in the conclusionin * 
in every hypothesisin *
(equivalent to in*  *
) everywherein (type of ident) (value of ident) … 
in type part ofident
, in the value part ofident
, etc.
For backward compatibility, the notation in ident+
performs
the conversion in hypotheses ident+
.

cbv flag*
¶

lazy flag*
¶

compute
¶ These parameterized reduction tactics apply to any goal and perform the normalization of the goal according to the specified flags. In correspondence with the kinds of reduction considered in Coq namely \(\beta\) (reduction of functional application), \(\delta\) (unfolding of transparent constants, see Controlling the reduction strategies and the conversion algorithm), \(\iota\) (reduction of patternmatching over a constructed term, and unfolding of
fix
andcofix
expressions) and \(\zeta\) (contraction of local definitions), the flags are eitherbeta
,delta
,match
,fix
,cofix
,iota
orzeta
. Theiota
flag is a shorthand formatch
,fix
andcofix
. Thedelta
flag itself can be refined intodelta qualid+
ordelta qualid+
, restricting in the first case the constants to unfold to the constants listed, and restricting in the second case the constant to unfold to all but the ones explicitly mentioned. Notice that thedelta
flag does not apply to variables bound by a letin construction inside theterm
itself (use here thezeta
flag). In any cases, opaque constants are not unfolded (see Controlling the reduction strategies and the conversion algorithm).Normalization according to the flags is done by first evaluating the head of the expression into a weakhead normal form, i.e. until the evaluation is bloked by a variable (or an opaque constant, or an axiom), as e.g. in
x u1 … un
, ormatch x with … end
, or(fix f x {struct x} := …) x
, or is a constructed form (a \(\lambda\)expression, a constructor, a cofixpoint, an inductive type, a product type, a sort), or is a redex that the flags prevent to reduce. Once a weakhead normal form is obtained, subterms are recursively reduced using the same strategy.Reduction to weakhead normal form can be done using two strategies: lazy (
lazy
tactic), or callbyvalue (cbv
tactic). The lazy strategy is a callbyneed strategy, with sharing of reductions: the arguments of a function call are weakly evaluated only when necessary, and if an argument is used several times then it is weakly computed only once. This reduction is efficient for reducing expressions with dead code. For instance, the proofs of a propositionexists x. P(x)
reduce to a pair of a witnesst
, and a proof thatt
satisfies the predicateP
. Most of the time,t
may be computed without computing the proof ofP(t)
, thanks to the lazy strategy.The callbyvalue strategy is the one used in ML languages: the arguments of a function call are systematically weakly evaluated first. Despite the lazy strategy always performs fewer reductions than the callbyvalue strategy, the latter is generally more efficient for evaluating purely computational expressions (i.e. with little dead code).

Variant
compute

Variant
cbv
These are synonyms for
cbv beta delta iota zeta
.

Variant
lazy
This is a synonym for
lazy beta delta iota zeta
.

Variant
compute qualid+

Variant
compute qualid+

Variant
lazy qualid+

Variant
lazy qualid+
These are respectively synonyms of
lazy beta delta qualid+ iota zeta
andlazy beta delta qualid+ iota zeta
.

Variant
vm_compute
¶ This tactic evaluates the goal using the optimized callbyvalue evaluation bytecodebased virtual machine described in [GregoireL02]. This algorithm is dramatically more efficient than the algorithm used for the
cbv
tactic, but it cannot be finetuned. It is specially interesting for full evaluation of algebraic objects. This includes the case of reflectionbased tactics.

Variant
native_compute
¶ This tactic evaluates the goal by compilation to Objective Caml as described in [BDenesGregoire11]. If Coq is running in native code, it can be typically two to five times faster than
vm_compute
. Note however that the compilation cost is higher, so it is worth using only for intensive computations.
Option
NativeCompute Profiling
¶ On Linux, if you have the
perf
profiler installed, this option makes it possible to profilenative_compute
evaluations.

Option
NativeCompute Profile Filename
¶ This option specifies the profile output; the default is
native_compute_profile.data
. The actual filename used will contain extra characters to avoid overwriting an existing file; that filename is reported to the user. That means you can individually profile multiple uses ofnative_compute
in a script. From the Linux command line, runperf report
on the profile file to see the results. Consult theperf
documentation for more details.

Option

Option
Debug Cbv
¶ This option makes
cbv
(and its derivativecompute
) print information about the constants it encounters and the unfolding decisions it makes.

red
¶ This tactic applies to a goal that has the form:
forall (x:T1) ... (xk:Tk), t
with
t
\(\beta\)\(\iota\)\(\zeta\)reducing toc t
_{1}… t
_{n} andc
a constant. Ifc
is transparent then it replacesc
with its definition (sayt
) and then reduces(t t
_{1}… t
_{n})
according to \(\beta\)\(\iota\)\(\zeta\)reduction rules.

Error
Not reducible
¶

hnf
¶ This tactic applies to any goal. It replaces the current goal with its head normal form according to the \(\beta\)\(\delta\)\(\iota\)\(\zeta\)reduction rules, i.e. it reduces the head of the goal until it becomes a product or an irreducible term. All inner \(\beta\)\(\iota\)redexes are also reduced.
Example: The term
forall n:nat, (plus (S n) (S n))
is not reduced byhnf
.
Note
The \(\delta\) rule only applies to transparent constants (see Controlling the reduction strategies and the conversion algorithm on transparency and opacity).

cbn
¶

simpl
¶ These tactics apply to any goal. They try to reduce a term to something still readable instead of fully normalizing it. They perform a sort of strong normalization with two key differences:
 They unfold a constant if and only if it leads to a \(\iota\)reduction, i.e. reducing a match or unfolding a fixpoint.
 While reducing a constant unfolding to (co)fixpoints, the tactics use the name of the constant the (co)fixpoint comes from instead of the (co)fixpoint definition in recursive calls.
The
cbn
tactic is claimed to be a more principled, faster and more predictable replacement forsimpl
.The
cbn
tactic accepts the same flags ascbv
andlazy
. The behavior of bothsimpl
andcbn
can be tuned using the Arguments vernacular command as follows:A constant can be marked to be never unfolded by
cbn
orsimpl
:Example
 Arguments minus n m : simpl never.
After that command an expression like
(minus (S x) y)
is left untouched by the tacticscbn
andsimpl
.A constant can be marked to be unfolded only if applied to enough arguments. The number of arguments required can be specified using the
/
symbol in the arguments list of theArguments
vernacular command.Example
 Definition fcomp A B C f (g : A > B) (x : A) : C := f (g x).
 fcomp is defined
 Notation “f \o g” := (fcomp f g) (at level 50).
 Arguments fcomp {A B C} f g x /.
After that command the expression
(f \o g)
is left untouched bysimpl
while((f \o g) t)
is reduced to(f (g t))
. The same mechanism can be used to make a constant volatile, i.e. always unfolded.Example
 Definition volatile := fun x : nat => x.
 volatile is defined
 Arguments volatile / x.
A constant can be marked to be unfolded only if an entire set of arguments evaluates to a constructor. The
!
symbol can be used to mark such arguments.Example
 Arguments minus !n !m.
After that command, the expression
(minus (S x) y)
is left untouched bysimpl
, while(minus (S x) (S y))
is reduced to(minus x y)
.A special heuristic to determine if a constant has to be unfolded can be activated with the following command:
Example
 Arguments minus n m : simpl nomatch.
The heuristic avoids to perform a simplification step that would expose a match construct in head position. For example the expression
(minus (S (S x)) (S y))
is simplified to(minus (S x) y)
even if an extra simplification is possible.
In detail, the tactic
simpl
first applies \(\beta\)\(\iota\)reduction. Then, it expands transparent constants and tries to reduce further using \(\beta\)\(\iota\) reduction. But, when no \(\iota\) rule is applied after unfolding then \(\delta\)reductions are not applied. For instance trying to usesimpl
on(plus n O) = n
changes nothing.Notice that only transparent constants whose name can be reused in the recursive calls are possibly unfolded by
simpl
. For instance a constant defined byplus’ := plus
is possibly unfolded and reused in the recursive calls, but a constant such assucc := plus (S O)
is never unfolded. This is the main difference betweensimpl
andcbn
. The tacticcbn
reduces whenever it will be able to reuse it or not:succ t
is reduced toS t
.

Variant
cbn qualid+

Variant
cbn qualid+
These are respectively synonyms of
cbn beta delta qualid+ iota zeta
andcbn beta delta qualid+ iota zeta
(seecbn
).

Variant
simpl pattern at num+
This applies
simpl
only to thenum+
occurrences of the subterms matchingpattern
in the current goal.
Error
Too few occurrences

Error

Variant
simpl qualid

Variant
simpl string
This applies
simpl
only to the applicative subterms whose head occurrence is the unfoldable constantqualid
(the constant can be referred to by its notation usingstring
if such a notation exists).

Variant
simpl string at num+
This applies
simpl
only to thenum+
applicative subterms whose head occurrence isqualid
(orstring
).

Option
Debug RAKAM
¶ This option makes
cbn
print various debugging information.RAKAM
is the Refolding Algebraic Krivine Abstract Machine.

unfold qualid
¶ This tactic applies to any goal. The argument qualid must denote a defined transparent constant or local definition (see Definitions and Controlling the reduction strategies and the conversion algorithm). The tactic
unfold
applies the \(\delta\) rule to each occurrence of the constant to whichqualid
refers in the current goal and then replaces it with its \(\beta\)\(\iota\)normal form.

Variant
unfold qualid in ident
Replaces
qualid
in hypothesisident
with its definition and replaces the hypothesis with its \(\beta\)\(\iota\) normal form.

Variant
unfold qualid+,
Replaces simultaneously
qualid+,
with their definitions and replaces the current goal with its \(\beta\)\(\iota\) normal form.

Variant
unfold qualid at num+,+,
The lists
num+,
specify the occurrences ofqualid
to be unfolded. Occurrences are located from left to right.

Variant
unfold string
If
string
denotes the discriminating symbol of a notation (e.g. “+”) or an expression defining a notation (e.g. “_ + _”), and this notation refers to an unfoldable constant, then the tactic unfolds it.

Variant
unfold string%key
This is variant of
unfold string
wherestring
gets its interpretation from the scope bound to the delimiting keykey
instead of its default interpretation (see Local interpretation rules for notations).

Variant
unfold qualid_or_string at num+,+,
This is the most general form, where
qualid_or_string
is either aqualid
or astring
referring to a notation.

fold term
¶ This tactic applies to any goal. The term
term
is reduced using thered
tactic. Every occurrence of the resultingterm
in the goal is then replaced byterm
.

pattern term
¶ This command applies to any goal. The argument
term
must be a free subterm of the current goal. The command pattern performs \(\beta\)expansion (the inverse of \(\beta\)reduction) of the current goal (sayT
) by replacing all occurrences of
term
inT
with a fresh variable  abstracting this variable
 applying the abstracted goal to
term
For instance, if the current goal
T
is expressible as \(\varphi\)(t)
where the notation captures all the instances oft
in \(\varphi\)(t)
, thenpattern t
transforms it into(fun x:A =>
\(\varphi\)(x)) t
. This command can be used, for instance, when the tacticapply
fails on matching. replacing all occurrences of

Variant
pattern term at num+
Only the occurrences
num+
ofterm
are considered for \(\beta\)expansion. Occurrences are located from left to right.

Variant
pattern term at  num+
All occurrences except the occurrences of indexes
num+
ofterm
are considered for \(\beta\)expansion. Occurrences are located from left to right.

Variant
pattern term+,
Starting from a goal \(\varphi\)
(t
_{1}… t
_{m})
, the tacticpattern t
_{1}, …, t
_{m} generates the equivalent goal(fun (x
_{1}:A
_{1}) … (x
_{m}:A
_{m}) =>
\(\varphi\)(x
_{1}… x
_{m})) t
_{1}… t
_{m}. Ift
_{i} occurs in one of the generated typesA
_{j} these occurrences will also be considered and possibly abstracted.

Variant
pattern term at num++,
This behaves as above but processing only the occurrences
num+
ofterm
starting fromterm
.

Variant
pattern term at ? num+,?+,
This is the most general syntax that combines the different variants.
Conversion tactics applied to hypotheses¶

conv_tactic in ident+,
Applies the conversion tactic
conv_tactic
to the hypothesesident+
. The tacticconv_tactic
is any of the conversion tactics listed in this section.If
ident
is a local definition, thenident
can be replaced by (Type ofident
) to address not the body but the type of the local definition.Example:
unfold not in (Type of H1) (Type of H3)
.

Error
No such hypothesis : ident.
Automation¶

auto
¶
This tactic implements a Prologlike resolution procedure to solve the current goal. It first tries to solve the goal using the assumption tactic, then it reduces the goal to an atomic one using intros and introduces the newly generated hypotheses as hints. Then it looks at the list of tactics associated to the head symbol of the goal and tries to apply one of them (starting from the tactics with lower cost). This process is recursively applied to the generated subgoals.
By default, auto only uses the hypotheses of the current goal and the hints of the database named core.

Variant
auto with ident+
Uses the hint databases
ident+
in addition to the database core. See The Hints Databases for auto and eauto for the list of predefined databases and the way to create or extend a database.

Variant
auto with *
Uses all existing hint databases. See The Hints Databases for auto and eauto

Variant
auto using lemma+
Uses
lemma+
in addition to hints (can be combined with the withident
option). Iflemma
is an inductive type, it is the collection of its constructors which is added as hints.

Variant
info_auto
Behaves like auto but shows the tactics it uses to solve the goal. This variant is very useful for getting a better understanding of automation, or to know what lemmas/assumptions were used.

Variant
debug auto
Behaves like
auto
but shows the tactics it tries to solve the goal, including failing paths.

Variant
info_?auto num? using lemma+? with ident+?
This is the most general form, combining the various options.

Variant
trivial
¶ This tactic is a restriction of auto that is not recursive and tries only hints that cost 0. Typically it solves trivial equalities like
X=X
.

Variant
trivial with ident+

Variant
trivial with *

Variant
trivial using lemma+

Variant
debug trivial

Variant
info_trivial
The following options enable printing of informative or debug information for
the auto
and trivial
tactics:

Option
Info Auto
¶

Option
Debug Auto
¶

Option
Info Trivial
¶

Option
Debug Trivial
¶
See also: The Hints Databases for auto and eauto

eauto
¶
This tactic generalizes auto
. While auto
does not try
resolution hints which would leave existential variables in the goal,
eauto
does try them (informally speaking, it usessimple eapply
where auto
uses simple apply
). As a consequence, eauto
can solve such a goal:
Example
 Hint Resolve ex_intro.
 the hint: eapply ex_intro will only be used by eauto
 Goal forall P:nat > Prop, P 0 > exists n, P n.
 1 subgoal ============================ forall P : nat > Prop, P 0 > exists n : nat, P n
 eauto.
 No more subgoals.
Note that ex_intro
should be declared as a hint.

Variant
info_?eauto num? using lemma+? with ident+?
The various options for eauto are the same as for auto.
eauto
also obeys the following options:

Option
Info Eauto
¶

Option
Debug Eauto
¶
See also: The Hints Databases for auto and eauto
This tactic unfolds constants that were declared through a Hint Unfold
in the given databases.

Variant
autounfold with ident+ in clause
Performs the unfolding in the given clause.

Variant
autounfold with *
Uses the unfold hints declared in all the hint databases.
This tactic [4] carries out rewritings according the rewriting rule
bases ident+
.
Each rewriting rule of a base ident
is applied to the main subgoal until
it fails. Once all the rules have been processed, if the main subgoal has
progressed (e.g., if it is distinct from the initial main goal) then the rules
of this base are processed again. If the main subgoal has not progressed then
the next base is processed. For the bases, the behavior is exactly similar to
the processing of the rewriting rules.
The rewriting rule bases are built with the Hint Rewrite vernacular
command.

Warning
This tactic may loop if you build non terminating rewriting systems.
¶

Variant
autorewrite with ident+ using tactic
Performs, in the same way, all the rewritings of the bases
ident+
applying tactic to the main subgoal after each rewriting step.

Variant
autorewrite with ident+ in qualid using tactic
Performs all the rewritings in hypothesis
qualid
applyingtactic
to the main subgoal after each rewriting step.

Variant
autorewrite with ident+ in clause
Performs all the rewriting in the clause
clause
. The clause argument must not contain anytype of
norvalue of
.
See also: HintRewrite for feeding the database of lemmas used by
autorewrite
.
See also: autorewrite
for examples showing the use of this tactic.

easy
¶ This tactic tries to solve the current goal by a number of standard closing steps. In particular, it tries to close the current goal using the closing tactics
trivial
, reflexivity, symmetry, contradiction and inversion of hypothesis. If this fails, it tries introducing variables and splitting andhypotheses, using the closing tactics afterwards, and splitting the goal usingsplit
and recursing.This tactic solves goals that belong to many common classes; in particular, many cases of unsatisfiable hypotheses, and simple equality goals are usually solved by this tactic.
Controlling automation¶
The hints databases for auto and eauto¶
The hints for auto
and eauto
are stored in databases. Each database
maps head symbols to a list of hints. One can use the command
to display the hints associated to the head symbol ident
(see Print Hint). Each hint has a cost that is a nonnegative
integer, and an optional pattern. The hints with lower cost are tried first. A
hint is tried by auto
when the conclusion of the current goal matches its
pattern or when it has no pattern.
Creating Hint databases¶
One can optionally declare a hint database using the command Create
HintDb
. If a hint is added to an unknown database, it will be
automatically created.
This command creates a new database named ident
. The database is
implemented by a Discrimination Tree (DT) that serves as an index of
all the lemmas. The DT can use transparency information to decide if a
constant should be indexed or not (c.f. The hints databases for auto and eauto),
making the retrieval more efficient. The legacy implementation (the default one
for new databases) uses the DT only on goals without existentials (i.e., auto
goals), for nonImmediate hints and do not make use of transparency
hints, putting more work on the unification that is run after
retrieval (it keeps a list of the lemmas in case the DT is not used).
The new implementation enabled by the discriminated option makes use
of DTs in all cases and takes transparency information into account.
However, the order in which hints are retrieved from the DT may differ
from the order in which they were inserted, making this implementation
observationally different from the legacy one.
The general command to add a hint to some databases ident+
is

Command
Hint hint_definition : ident+
¶ 
Variant
Hint hint_definition
No database name is given: the hint is registered in the core database.

Variant
Local Hint hint_definition : ident+
This is used to declare hints that must not be exported to the other modules that require and import the current module. Inside a section, the option Local is useless since hints do not survive anyway to the closure of sections.

Variant
Local Hint hint_definition
Idem for the core database.
This command adds
simple apply term
to the hint list with the head symbol of the type ofterm
. The cost of that hint is the number of subgoals generated bysimple apply term
ornum
if specified. The associatedpattern
is inferred from the conclusion of the type ofterm
or the givenpattern
if specified. In case the inferred type ofterm
does not start with a product the tactic added in the hint list isexact term
. In case this type can however be reduced to a type starting with a product, the tacticsimple apply term
is also stored in the hints list. If the inferred type ofterm
contains a dependent quantification on a variable which occurs only in the premisses of the type and not in its conclusion, no instance could be inferred for the variable by unification with the goal. In this case, the hint is added to the hint list ofeauto
instead of the hint list of auto and a warning is printed. A typical example of a hint that is used only byeauto
is a transitivity lemma.
Error
term cannot be used as a hint
¶ The head symbol of the type of
term
is a bound variable such that this tactic cannot be associated to a constant.

Variant
Hint Resolve > term
Adds the lefttoright implication of an equivalence as a hint (informally the hint will be used as
apply < term
, although as mentionned before, the tactic actually used is a restricted version ofapply
).

Variant
Resolve < term
Adds the righttoleft implication of an equivalence as a hint.

Variant
Hint Immediate term
¶ This command adds
simple apply term; trivial
to the hint list associated with the head symbol of the type ofident
in the given database. This tactic will fail if all the subgoals generated bysimple apply term
are not solved immediately by thetrivial
tactic (which only tries tactics with cost 0).This command is useful for theorems such as the symmetry of equality orn+1=m+1 > n=m
that we may like to introduce with a limited use in order to avoid useless proofsearch. The cost of this tactic (which never generates subgoals) is always 1, so that it is not used bytrivial
itself.

Error
term cannot be used as a hint

Variant
Hint Constructors ident
¶ If
ident
is an inductive type, this command adds all its constructors as hints of typeResolve
. Then, when the conclusion of current goal has the form(ident …)
,auto
will try to apply each constructor.

Variant
Hint Unfold qualid
¶ This adds the tactic
unfold qualid
to the hint list that will only be used when the head constant of the goal isident
. Its cost is 4.

Variant
Hint Transparent Opaque qualid

Variant
:name: Hint ( Transparent  Opaque )
 This adds a transparency hint to the database, making
qualid
a transparent or opaque constant during resolution. This information is used during unification of the goal with any lemma in the database and inside the discrimination network to relax or constrain it in the case of discriminated databases.
Variant
Hint %(Transparent  Opaque) ident+
Declares each
ident
as a transparent or opaque constant.

Variant
Hint Extern num pattern? => tactic
This hint type is to extend
auto
with tactics other thanapply
andunfold
. For that, we must specify a cost, an optionalpattern
and atactic
to execute.Example
 Hint Extern 4 (~(_ = _)) => discriminate.
Now, when the head of the goal is a disequality,
auto
will try discriminate if it does not manage to solve the goal with hints with a cost less than 4. One can even use some subpatterns of the pattern in the tactic script. A subpattern is a question mark followed by an identifier, like?X1
or?X2
. Here is an example:Example
 Require Import List.
 Hint Extern 5 ({?X1 = ?X2} + {?X1 <> ?X2}) => generalize X1, X2; decide equality : eqdec.
 Goal forall a b:list (nat * nat), {a = b} + {a <> b}.
 1 subgoal ============================ forall a b : list (nat * nat), {a = b} + {a <> b}
 Info 1 auto with eqdec.
 <ltac_plugin::auto@0> eqdec No more subgoals.

Variant
Hint Cut regexp
Warning
These hints currently only apply to typeclass proof search and the
typeclasses eauto
tactic.This command can be used to cut the proofsearch tree according to a regular expression matching paths to be cut. The grammar for regular expressions is the following. Beware, there is no operator precedence during parsing, one can check with
Print HintDb
to verify the current cut expression:e ::= ident hint or instance identifier _ any hint  e\e′ disjunction  e e′ sequence  e * Kleene star  emp empty  eps epsilon  ( e )
The emp regexp does not match any search path while eps matches the empty path. During proof search, the path of successive successful hints on a search branch is recorded, as a list of identifiers for the hints (note Hint Extern’s do not have an associated identifier). Before applying any hint
ident
the current path p extended withident
is matched against the current cut expression c associated to the hint database. If matching succeeds, the hint is not applied. The semantics ofHint Cut e
is to set the cut expression toc  e
, the initial cut expression being emp.

Variant
Hint Mode qualid (+  !  )*
This sets an optional mode of use of the identifier
qualid
. When proofsearch faces a goal that ends in an application ofqualid
to argumentsterm … term
, the mode tells if the hints associated toqualid
can be applied or not. A mode specification is a list of n+
,!
or
items that specify if an argument of the identifier is to be treated as an input (+
), if its head only is an input (!
) or an output (
) of the identifier. For a mode to match a list of arguments, input terms and input heads must not contain existential variables or be existential variables respectively, while outputs can be any term. Multiple modes can be declared for a single identifier, in that case only one mode needs to match the arguments for the hints to be applied.The head of a term is understood here as the applicative head, or the match or projection scrutinee’s head, recursively, casts being ignored.Hint Mode
is especially useful for typeclasses, when one does not want to support default instances and avoid ambiguity in general. Setting a parameter of a class as an input forces proofsearch to be driven by that index of the class, with!
giving more flexibility by allowing existentials to still appear deeper in the index but not at its head.
Note
One can use an
Extern
hint with no pattern to do patternmatching on hypotheses usingmatch goal
with inside the tactic. 
Variant

Variant
Hint databases defined in the Coq standard library¶
Several hint databases are defined in the Coq standard library. The actual content of a database is the collection of the hints declared to belong to this database in each of the various modules currently loaded. Especially, requiring new modules potentially extend a database. At Coq startup, only the core database is non empty and can be used.
core:  This special database is automatically used by auto , except when
pseudodatabase nocore is given to auto . The core database
contains only basic lemmas about negation, conjunction, and so on from.
Most of the hints in this database come from the Init and Logic directories. 

arith:  This database contains all lemmas about Peano’s arithmetic proved in the directories Init and Arith. 
zarith:  contains lemmas about binary signed integers from the directories
theories/ZArith. When required, the module Omega also extends the
database zarith with a highcost hint that calls omega on equations
and inequalities in nat or Z. 
bool:  contains lemmas about booleans, mostly from directory theories/Bool. 
datatypes:  is for lemmas about lists, streams and so on that are mainly proved in the Lists subdirectory. 
sets:  contains lemmas about sets and relations from the directories Sets and Relations. 
typeclass_instances:  
contains all the type class instances declared in the
environment, including those used for setoid_rewrite ,
from the Classes directory. 
You are advised not to put your own hints in the core database, but use one or several databases specific to your development.
This command removes the hints associated to terms term+
in databases
ident+
.

Command
Print Hint
This command displays all hints that apply to the current goal. It fails if no proof is being edited, while the two variants can be used at every moment.
Variants:

Command
Print Hint ident
This command displays only tactics associated with
ident
in the hints list. This is independent of the goal being edited, so this command will not fail if no goal is being edited.

Command
Print Hint *
This command displays all declared hints.

Command
Hint Rewrite term+ : ident+
¶ This vernacular command adds the terms
term+
(their types must be equalities) in the rewriting basesident+
with the default orientation (left to right). Notice that the rewriting bases are distinct from theauto
hint bases and thatauto does not take them into account.This command is synchronous with the section mechanism (see Section mechanism): when closing a section, all aliases created by
Hint Rewrite
in that section are lost. Conversely, when loading a module, allHint Rewrite
declarations at the global level of that module are loaded.
Variants:

Command
Hint Rewrite > term+ : ident+
This is strictly equivalent to the command above (we only make explicit the orientation which otherwise defaults to >).

Command
Hint Rewrite < term+ : ident+
Adds the rewriting rules
term+
with a righttoleft orientation in the basesident+
.
Hint locality¶
Hints provided by the Hint
commands are erased when closing a section.
Conversely, all hints of a module A
that are not defined inside a
section (and not defined with option Local
) become available when the
module A
is imported (using e.g. Require Import A.
).
As of today, hints only have a binary behavior regarding locality, as
described above: either they disappear at the end of a section scope,
or they remain global forever. This causes a scalability issue,
because hints coming from an unrelated part of the code may badly
influence another development. It can be mitigated to some extent
thanks to the Remove Hints
command (see Remove Hints),
but this is a mere workaround and has some limitations (for instance, external
hints cannot be removed).
A proper way to fix this issue is to bind the hints to their module scope, as
for most of the other objects Coq uses. Hints should only made available when
the module they are defined in is imported, not just required. It is very
difficult to change the historical behavior, as it would break a lot of scripts.
We propose a smooth transitional path by providing the Loose Hint Behavior
option which accepts three flags allowing for a finegrained handling of
nonimported hints.

Option
Loose Hint Behavior “Lax” “Warn” “Strict”
¶ This option accepts three values, which control the behavior of hints w.r.t.
Import
: “Lax”: this is the default, and corresponds to the historical behavior, that is, hints defined outside of a section have a global scope.
 “Warn”: outputs a warning when a nonimported hint is used. Note that this is an overapproximation, because a hint may be triggered by a run that will eventually fail and backtrack, resulting in the hint not being actually useful for the proof.
 “Strict”: changes the behavior of an unloaded hint to a immediate fail tactic, allowing to emulate an importscoped hint mechanism.
Setting implicit automation tactics¶

Command
Proof with tactic
¶ This command may be used to start a proof. It defines a default tactic to be used each time a tactic command
tactic
_{1} is ended by...
. In this case the tactic command typed by the user is equivalent totactic
_{1};tactic
.See also:
Proof.
in Switching on/off the proof editing mode.
Variant
Proof with tactic using ident+
Combines in a single line
Proof with
andProof using
, see Switching on/off the proof editing mode

Variant
Proof using ident+ with tactic
Combines in a single line
Proof with
andProof using
, see Switching on/off the proof editing mode

Command
Declare Implicit Tactic tactic
¶ This command declares a tactic to be used to solve implicit arguments that Coq does not know how to solve by unification. It is used every time the term argument of a tactic has one of its holes not fully resolved.
Example
 Parameter quo : nat > forall n:nat, n<>0 > nat.
 quo is declared
 Notation “x // y” := (quo x y _) (at level 40).
 Declare Implicit Tactic assumption.
 Goal forall n m, m<>0 > { q:nat & { r  q * m + r = n } }.
 quo is declared 1 subgoal ============================ forall n m : nat, m <> 0 > {q : nat & {r : nat  q * m + r = n}}
 intros.
 1 subgoal n, m : nat H : m <> 0 ============================ {q : nat & {r : nat  q * m + r = n}}
 exists (n // m).
 1 subgoal n, m : nat H : m <> 0 ============================ {r : nat  n // m * m + r = n}
The tactic
exists (n // m)
did not fail. The hole was solved byassumption
so that it behaved asexists (quo n m H)
.
Variant
Decision procedures¶

tauto
¶
This tactic implements a decision procedure for intuitionistic propositional
calculus based on the contractionfree sequent calculi LJT* of Roy Dyckhoff
[Dyc92]. Note that tauto
succeeds on any instance of an
intuitionistic tautological proposition. tauto
unfolds negations and
logical equivalence but does not unfold any other definition.
The following goal can be proved by tauto
whereas auto
would
fail:
Example
 Goal forall (x:nat) (P:nat > Prop), x = 0 \/ P x > x <> 0 > P x.
 1 subgoal ============================ forall (x : nat) (P : nat > Prop), x = 0 \/ P x > x <> 0 > P x
 intros.
 1 subgoal x : nat P : nat > Prop H : x = 0 \/ P x H0 : x <> 0 ============================ P x
 tauto.
 No more subgoals.
Moreover, if it has nothing else to do, tauto
performs introductions.
Therefore, the use of intros
in the previous proof is unnecessary.
tauto
can for instance for:
Example
 Goal forall (A:Prop) (P:nat > Prop), A \/ (forall x:nat, ~ A > P x) > forall x:nat, ~ A > P x.
 1 subgoal ============================ forall (A : Prop) (P : nat > Prop), A \/ (forall x : nat, ~ A > P x) > forall x : nat, ~ A > P x
 tauto.
 No more subgoals.
Note
In contrast, tauto
cannot solve the following goal
Goal forall (A:Prop) (P:nat > Prop), A \/ (forall x:nat, ~ A > P x) >
forall x:nat, ~ ~ (A \/ P x).
because (forall x:nat, ~ A > P x)
cannot be treated as atomic and
an instantiation of x is necessary.

Variant
dtauto
¶ While
tauto
recognizes inductively defined connectives isomorphic to the standard connectiveand, prod, or, sum, False, Empty_set, unit, True
,dtauto
recognizes also all inductive types with one constructors and no indices, i.e. recordstyle connectives.
The tactic intuition
takes advantage of the searchtree built by the
decision procedure involved in the tactic tauto
. It uses this
information to generate a set of subgoals equivalent to the original one (but
simpler than it) and applies the tactic tactic
to them [Mun94]. If
this tactic fails on some goals then intuition
fails. In fact,
tauto
is simply intuition fail
.
For instance, the tactic intuition auto
applied to the goal
(forall (x:nat), P x)/\B > (forall (y:nat),P y)/\ P O \/B/\ P O
internally replaces it by the equivalent one:
(forall (x:nat), P x), B  P O
and then uses auto
which completes the proof.
Originally due to César Muñoz, these tactics (tauto
and
intuition
) have been completely reengineered by David Delahaye using
mainly the tactic language (see The tactic language). The code is
now much shorter and a significant increase in performance has been noticed.
The general behavior with respect to dependent types, unfolding and
introductions has slightly changed to get clearer semantics. This may lead to
some incompatibilities.

Variant
intuition
Is equivalent to
intuition auto with *
.

Variant
dintuition
While
intuition
recognizes inductively defined connectives isomorphic to the standard connectiveand, prod, or, sum, False, Empty_set, unit, True
,dintuition
recognizes also all inductive types with one constructors and no indices, i.e. recordstyle connectives.

Option
Intuition Negation Unfolding
¶ Controls whether
intuition
unfolds inner negations which do not need to be unfolded. This option is on by default.

rtauto
¶
The rtauto
tactic solves propositional tautologies similarly to what
tauto
does. The main difference is that the proof term is built using a
reflection scheme applied to a sequent calculus proof of the goal. The search
procedure is also implemented using a different technique.
Users should be aware that this difference may result in faster proof search
but slower proofchecking, and rtauto
might not solve goals that
tauto
would be able to solve (e.g. goals involving universal
quantifiers).

firstorder
¶
The tactic firstorder
is an experimental extension of tauto
to
first order reasoning, written by Pierre Corbineau. It is not restricted to
usual logical connectives but instead may reason about any firstorder class
inductive definition.

Option
Firstorder Solver
¶ The default tactic used by
firstorder
when no rule applies isauto with *
, it can be reset locally or globally using this option and printed usingPrint Firstorder Solver
.

Variant
firstorder using qualid+
Adds lemmas
qualid+
to the proofsearch environment. Ifqualid
refers to an inductive type, it is the collection of its constructors which are added to the proofsearch environment.

Variant
firstorder with ident+
Adds lemmas from
auto
hint basesident+
to the proofsearch environment.

Variant
firstorder tactic using qualid+ with ident+
This combines the effects of the different variants of
firstorder
.

congruence
¶
The tactic congruence
, by Pierre Corbineau, implements the standard
Nelson and Oppen congruence closure algorithm, which is a decision procedure
for ground equalities with uninterpreted symbols. It also include the
constructor theory (see injection
and discriminate
). If the goal
is a nonquantified equality, congruence tries to prove it with nonquantified
equalities in the context. Otherwise it tries to infer a discriminable equality
from those in the context. Alternatively, congruence tries to prove that a
hypothesis is equal to the goal or to the negation of another hypothesis.
congruence
is also able to take advantage of hypotheses stating
quantified equalities, you have to provide a bound for the number of extra
equalities generated that way. Please note that one of the members of the
equality must contain all the quantified variables in order for congruence to
match against it.
Example
 Theorem T (A:Type) (f:A > A) (g: A > A > A) a b: a=(f a) > (g b (f a))=(f (f a)) > (g a b)=(f (g b a)) > (g a b)=a.
 1 subgoal A : Type f : A > A g : A > A > A a, b : A ============================ a = f a > g b (f a) = f (f a) > g a b = f (g b a) > g a b = a
 intros.
 1 subgoal A : Type f : A > A g : A > A > A a, b : A H : a = f a H0 : g b (f a) = f (f a) H1 : g a b = f (g b a) ============================ g a b = a
 congruence.
 No more subgoals.
 Qed.
 T is defined
 Theorem inj (A:Type) (f:A > A * A) (a c d: A) : f = pair a > Some (f c) = Some (f d) > c=d.
 1 subgoal A : Type f : A > A * A a, c, d : A ============================ f = pair a > Some (f c) = Some (f d) > c = d
 intros.
 1 subgoal A : Type f : A > A * A a, c, d : A H : f = pair a H0 : Some (f c) = Some (f d) ============================ c = d
 congruence.
 No more subgoals.
 Qed.
 inj is defined

Variant
congruence n
Tries to add at most n instances of hypotheses stating quantified equalities to the problem in order to solve it. A bigger value of n does not make success slower, only failure. You might consider adding some lemmas as hypotheses using assert in order for
congruence
to use them.

Variant
congruence with term+
Adds
term+
to the pool of terms used bycongruence
. This helps in case you have partially applied constructors in your goal.

Error
I don’t know how to handle dependent equality
¶ The decision procedure managed to find a proof of the goal or of a discriminable equality but this proof could not be built in Coq because of dependentlytyped functions.

Error
Goal is solvable by congruence but some arguments are missing. Try congruence with …, replacing metavariables by arbitrary terms.
¶ The decision procedure could solve the goal with the provision that additional arguments are supplied for some partially applied constructors. Any term of an appropriate type will allow the tactic to successfully solve the goal. Those additional arguments can be given to congruence by filling in the holes in the terms given in the error message, using the with variant described above.

Option
Congruence Verbose
¶ This option makes
congruence
print debug information.
Checking properties of terms¶
Each of the following tactics acts as the identity if the check succeeds, and results in an error otherwise.

constr_eq term term
¶ This tactic checks whether its arguments are equal modulo alpha conversion and casts.

Error
Not equal
¶

unify term term
¶ This tactic checks whether its arguments are unifiable, potentially instantiating existential variables.

Error
Not unifiable
¶

Variant
unify term term with ident
Unification takes the transparency information defined in the hint database
ident
into account (see the hints databases for auto and eauto).

is_evar term
¶ This tactic checks whether its argument is a current existential variable. Existential variables are uninstantiated variables generated by
eapply
and some other tactics.

Error
Not an evar
¶

has_evar term
¶ This tactic checks whether its argument has an existential variable as a subterm. Unlike context patterns combined with
is_evar
, this tactic scans all subterms, including those under binders.

Error
No evars
¶

is_var term
¶ This tactic checks whether its argument is a variable or hypothesis in the current goal context or in the opened sections.

Error
Not a variable or hypothesis
¶
Equality¶

f_equal
¶
This tactic applies to a goal of the form f a
_{1} … a
_{n}
= f′a′
_{1} … a′
_{n}. Using f_equal
on such a goal
leads to subgoals f=f′
and a
_{1} = a′
_{1} and so on up
to a
_{n} = a′
_{n}. Amongst these subgoals, the simple ones
(e.g. provable by reflexivity
or congruence
) are automatically
solved by f_equal
.

reflexivity
¶
This tactic applies to a goal that has the form t=u
. It checks that t
and u are convertible and then solves the goal. It is equivalent to apply
refl_equal
.

Error
The conclusion is not a substitutive equation
¶

Error
Unable to unify … with …

symmetry
¶
This tactic applies to a goal that has the form t=u
and changes it into
u=t
.

Variant
symmetry in ident
If the statement of the hypothesis ident has the form
t=u
, the tactic changes it tou=t
.
This tactic applies to a goal that has the form t=u
and transforms it
into the two subgoals t=term
and term=u
.
Equality and inductive sets¶
We describe in this section some special purpose tactics dealing with
equality and inductive sets or types. These tactics use the
equality eq:forall (A:Type), A>A>Prop
, simply written with the infix
symbol =
.

decide equality
¶ This tactic solves a goal of the form
forall x y:R, {x=y}+{ ~x=y}
, whereR
is an inductive type such that its constructors do not take proofs or functions as arguments, nor objects in dependent types. It solves goals of the form{x=y}+{ ~x=y}
as well.

compare term term
¶ This tactic compares two given objects
term
andterm
of an inductive datatype. IfG
is the current goal, it leaves the sub goalsterm =term > G
and~ term = term > G
. The type ofterm
andterm
must satisfy the same restrictions as in the tacticdecide equality
.

simplify_eq term
¶ Let
term
be the proof of a statement of conclusionterm = term
. Ifterm
andterm
are structurally different (in the sense described for the tacticdiscriminate
), then the tacticsimplify_eq
behaves asdiscriminate term
, otherwise it behaves asinjection term
.
Note
If some quantified hypothesis of the goal is named ident
,
then simplify_eq ident
first introduces the hypothesis in the local
context using intros until ident
.

Variant
simplify_eq num
This does the same thing as
intros until num
thensimplify_eq ident
whereident
is the identifier for the last introduced hypothesis.

Variant
simplify_eq term with bindings_list
This does the same as
simplify_eq term
but using the given bindings to instantiate parameters or hypotheses ofterm
.

Variant
esimplify_eq num

Variant
esimplify_eq term with bindings_list?
¶ This works the same as
simplify_eq
but if the type ofterm
, or the type of the hypothesis referred to bynum
, has uninstantiated parameters, these parameters are left as existential variables.

Variant
simplify_eq
If the current goal has form
t1 <> t2
, it behaves asintro ident; simplify_eq ident
.

dependent rewrite > ident
¶ This tactic applies to any goal. If
ident
has type(existT B a b)=(existT B a’ b’)
in the local context (i.e. eachterm
of the equality has a sigma type{ a:A & (B a)}
) this tactic rewritesa
intoa’
andb
intob’
in the current goal. This tactic works even ifB
is also a sigma type. This kind of equalities between dependent pairs may be derived by theinjection
andinversion
tactics.

Variant
dependent rewrite < ident
Analogous to
dependent rewrite >
but uses the equality from right to left.
Inversion¶
functional inversion
is a tactic that performs inversion on hypothesis
ident
of the form qualid term+ = term
or term = qualid
term+
where qualid
must have been defined using Function (see
Advanced recursive functions). Note that this tactic is only
available after a Require Import FunInd
.

Error
Cannot find inversion information for hypothesis ident
¶ This error may be raised when some inversion lemma failed to be generated by Function.

Variant
functional inversion num
This does the same thing as intros until num thenfunctional inversion ident where ident is the identifier for the last introduced hypothesis.

Variant
functional inversion ident qualid

Variant
functional inversion num qualid
If the hypothesis
ident
(ornum
) has a type of the formqualid
_{1}term
_{1} …term
_{n}= qualid
_{2}term
_{n+1} …term
_{n+m} wherequalid
_{1} andqualid
_{2} are valid candidates to functional inversion, this variant allows choosing whichqualid
is inverted.
This kind of inversion has nothing to do with the tactic inversion
above. This tactic does change (@ident t)
, where t is a term built in
order to ensure the convertibility. In other words, it does inversion of the
function ident
. This function must be a fixpoint on a simple recursive
datatype: see quote for the full details.

Error
quote: not a simple fixpoint
¶ Happens when quote is not able to perform inversion properly.
Classical tactics¶
In order to ease the proving process, when the Classical module is
loaded. A few more tactics are available. Make sure to load the module
using the Require Import
command.

classical_left
¶

Variant
classical_right
¶ The tactics
classical_left
andclassical_right
are the analog of the left and right but using classical logic. They can only be used for disjunctions. Useclassical_left
to prove the left part of the disjunction with the assumption that the negation of right part holds. Useclassical_right
to prove the right part of the disjunction with the assumption that the negation of left part holds.
Automatizing¶

btauto
¶
The tactic btauto
implements a reflexive solver for boolean
tautologies. It solves goals of the form t = u
where t and u are
constructed over the following grammar:
t ::= x ∣ true ∣ false ∣ orb t1 t2 ∣ andb t1 t2 ∣ xorb t1 t2 ∣ negb t ∣ if t1 then t2 else t3Whenever the formula supplied is not a tautology, it also provides a counterexample.
Internally, it uses a system very similar to the one of the ring tactic.

omega
¶
The tactic omega
, due to Pierre Crégut, is an automatic decision
procedure for Presburger arithmetic. It solves quantifierfree
formulas built with ~, /, /`, `> on top of equalities,
inequalities and disequalities on both the type nat
of natural numbers
and Z
of binary integers. This tactic must be loaded by the command
Require Import Omega
. See the additional documentation about omega
(see Chapter Omega: a solver for quantifierfree problems in Presburger Arithmetic).

ring
¶
The ring
tactic solves equations upon polynomial expressions of a ring
(or semiring) structure. It proceeds by normalizing both hand sides
of the equation (w.r.t. associativity, commutativity and
distributivity, constant propagation) and comparing syntactically the
results.
ring_simplify
applies the normalization procedure described above to
the terms given. The tactic then replaces all occurrences of the terms
given in the conclusion of the goal by their normal forms. If no term
is given, then the conclusion should be an equation and both hand
sides are normalized.
See The ring and field tactic families for more information on
the tactic and how to declare new ring structures. All declared field structures
can be printed with the Print Rings
command.

field
¶

field_simplify_eq
¶
The field tactic is built on the same ideas as ring: this is a reflexive tactic that solves or simplifies equations in a field structure. The main idea is to reduce a field expression (which is an extension of ring expressions with the inverse and division operations) to a fraction made of two polynomial expressions.
Tactic field
is used to solve subgoals, whereas field_simplify term+
replaces the provided terms by their reduced fraction.
field_simplify_eq
applies when the conclusion is an equation: it
simplifies both hand sides and multiplies so as to cancel
denominators. So it produces an equation without division nor inverse.
All of these 3 tactics may generate a subgoal in order to prove that denominators are different from zero.
See The ring and field tactic families for more information on the tactic and how to declare new field structures. All declared field structures can be printed with the Print Fields command.
Example
 Require Import Reals.
 [Loading ML file z_syntax_plugin.cmxs … done] [Loading ML file r_syntax_plugin.cmxs … done] [Loading ML file quote_plugin.cmxs … done] [Loading ML file newring_plugin.cmxs … done] [Loading ML file omega_plugin.cmxs … done] [Loading ML file fourier_plugin.cmxs … done] [Loading ML file micromega_plugin.cmxs … done]
 Goal forall x y:R, (x * y > 0)%R > (x * (1 / x + x / (x + y)))%R = (( 1 / y) * y * ( x * (x / (x + y))  1))%R.
 1 subgoal ============================ forall x y : R, (x * y > 0)%R > (x * (1 / x + x / (x + y)))%R = (1 / y * y * ( x * (x / (x + y))  1))%R
 intros; field.
 1 subgoal x, y : R H : (x * y > 0)%R ============================ (x + y)%R <> 0%R /\ y <> 0%R /\ x <> 0%R
See also: file plugins/setoid_ring/RealField.v for an example of instantiation, theory theories/Reals for many examples of use of field.

fourier
¶
This tactic written by Loïc Pottier solves linear inequalities on real
numbers using Fourier’s method [Fou90]. This tactic must be loaded by
Require Import Fourier
.
Example
 Require Import Reals.
 Require Import Fourier.
 Goal forall x y:R, (x < y)%R > (y + 1 >= x  1)%R.
 1 subgoal ============================ forall x y : R, x < y > y + 1 >= x  1
 intros; fourier.
 No more subgoals.
Nonlogical tactics¶

cycle num
¶ This tactic puts the
num
first goals at the end of the list of goals. Ifnum
is negative, it will put the last \(num\) goals at the beginning of the list.
Example
 Parameter P : nat > Prop.
 P is declared
 Goal P 1 /\ P 2 /\ P 3 /\ P 4 /\ P 5.
 1 subgoal ============================ P 1 /\ P 2 /\ P 3 /\ P 4 /\ P 5
 repeat split.
 5 subgoals ============================ P 1 subgoal 2 is: P 2 subgoal 3 is: P 3 subgoal 4 is: P 4 subgoal 5 is: P 5
 all: cycle 2.
 5 subgoals ============================ P 3 subgoal 2 is: P 4 subgoal 3 is: P 5 subgoal 4 is: P 1 subgoal 5 is: P 2
 all: cycle 3.
 5 subgoals ============================ P 5 subgoal 2 is: P 1 subgoal 3 is: P 2 subgoal 4 is: P 3 subgoal 5 is: P 4

swap num num
¶ This tactic switches the position of the goals of indices
num
andnum
. If eithernum
ornum
is negative then goals are counted from the end of the focused goal list. Goals are indexed from 1, there is no goal with position 0.
Example
 Parameter P : nat > Prop.
 P is declared
 Goal P 1 /\ P 2 /\ P 3 /\ P 4 /\ P 5.
 1 subgoal ============================ P 1 /\ P 2 /\ P 3 /\ P 4 /\ P 5
 repeat split.
 5 subgoals ============================ P 1 subgoal 2 is: P 2 subgoal 3 is: P 3 subgoal 4 is: P 4 subgoal 5 is: P 5
 all: swap 1 3.
 5 subgoals ============================ P 3 subgoal 2 is: P 2 subgoal 3 is: P 1 subgoal 4 is: P 4 subgoal 5 is: P 5
 all: swap 1 1.
 5 subgoals ============================ P 5 subgoal 2 is: P 2 subgoal 3 is: P 1 subgoal 4 is: P 4 subgoal 5 is: P 3

revgoals
¶
This tactics reverses the list of the focused goals.
Example
 Parameter P : nat > Prop.
 P is declared
 Goal P 1 /\ P 2 /\ P 3 /\ P 4 /\ P 5.
 1 subgoal ============================ P 1 /\ P 2 /\ P 3 /\ P 4 /\ P 5
 repeat split.
 5 subgoals ============================ P 1 subgoal 2 is: P 2 subgoal 3 is: P 3 subgoal 4 is: P 4 subgoal 5 is: P 5
 all: revgoals.
 5 subgoals ============================ P 5 subgoal 2 is: P 4 subgoal 3 is: P 3 subgoal 4 is: P 2 subgoal 5 is: P 1

shelve
¶ This tactic moves all goals under focus to a shelf. While on the shelf, goals will not be focused on. They can be solved by unification, or they can be called back into focus with the command
Unshelve
.

Variant
shelve_unifiable
Shelves only the goals under focus that are mentioned in other goals. Goals that appear in the type of other goals can be solved by unification.
Example
 Goal exists n, n=0.
 1 subgoal ============================ exists n : nat, n = 0
 refine (ex_intro _ _ _).
 1 focused subgoal (shelved: 1) ============================ ?Goal = 0
 all:shelve_unifiable.
 reflexivity.
 No more subgoals.

Command
Unshelve
¶ This command moves all the goals on the shelf (see
shelve
) from the shelf into focus, by appending them to the end of the current list of focused goals.

give_up
¶ This tactic removes the focused goals from the proof. They are not solved, and cannot be solved later in the proof. As the goals are not solved, the proof cannot be closed.
The
give_up
tactic can be used while editing a proof, to choose to write the proof script in a nonsequential order.