(* This script shows, in two different ways, the inconsistency of the propositional extensionality axiom with the guard condition for cofixpoints. It is the dual of the problem on fixpoints (cf subterm.v, subterm2.v, subterm3.v). Posted on Coq-club by Maxime Dénès (02/26/2014). *)
(* First example *)
CoInductive CoFalse : Prop := CF : CoFalse -> False -> CoFalse.
CoInductive Pandora : Prop := C : CoFalse -> Pandora.

Axiom prop_ext : forall P Q : Prop, (P<->Q) -> P = Q.