Library Coq.Logic.PropExtensionality
This module states propositional extensionality and draws
consequences of it
Axiom propositional_extensionality :
forall (P Q : Prop), (P <-> Q) -> P = Q.
Require Import ClassicalFacts.
Theorem proof_irrelevance : forall (P:Prop) (p1 p2:P), p1 = p2.