# Library Coq.QArith.Qfield

Require Export Field.
Require Export QArith_base.
Require Import NArithRing.

# field and ring tactics for rational numbers

Definition Qsrt : ring_theory 0 1 Qplus Qmult Qminus Qopp Qeq.

Definition Qsft : field_theory 0 1 Qplus Qmult Qminus Qopp Qdiv Qinv Qeq.

Lemma Qpower_theory : power_theory 1 Qmult Qeq Z.of_N Qpower.

Ltac isQcst t :=
match t with
| inject_Z ?z => isZcst z
| Qmake ?n ?d =>
match isZcst n with
true => isPcst d
| _ => false
end
| _ => false
end.

Ltac Qcst t :=
match isQcst t with
true => t
| _ => NotConstant
end.

Ltac Qpow_tac t :=
match t with
| Z0 => N0
| Zpos ?n => Ncst (Npos n)
| Z.of_N ?n => Ncst n
| NtoZ ?n => Ncst n
| _ => NotConstant
end.

Add Field Qfield : Qsft
(decidable Qeq_bool_eq,
completeness Qeq_eq_bool,
constants [Qcst],
power_tac Qpower_theory [Qpow_tac]).

Exemple of use:

Section Examples.

Let ex1 : forall x y z : Q, (x+y)*z == (x*z)+(y*z).
Qed.

Let ex2 : forall x y : Q, x+y == y+x.
Qed.

Let ex3 : forall x y z : Q, (x+y)+z == x+(y+z).
Qed.

Let ex4 : (inject_Z 1)+(inject_Z 1)==(inject_Z 2).
Qed.

Let ex5 : 1+1 == 2#1.
Qed.

Let ex6 : (1#1)+(1#1) == 2#1.
Qed.

Let ex7 : forall x : Q, x-x== 0.
Qed.

Let ex8 : forall x : Q, x^1 == x.
Qed.

Let ex9 : forall x : Q, x^0 == 1.
Qed.

Let ex10 : forall x y : Q, ~(y==0) -> (x/y)*y == x.
Qed.

End Examples.

Lemma Qopp_plus : forall a b, -(a+b) == -a + -b.

Lemma Qopp_opp : forall q, - -q==q.