proposition: Lemma ext_prop_fixpoint : prop_extensionality -> forall A:Prop, inhabited A -> has_fixpoint A.
proof: Proof. intros Ext A a. case (prop_ext_retract_A_A_imp_A Ext A a); intros g1 g2 g1_o_g2. exists (fun f => (fun x:A => f (g1 x x)) (g2 (fun x => f (g1 x x)))). intro f. pattern (g1 (g2 (fun x:A => f (g1 x x)))) at 1. rewrite (g1_o_g2 (fun x:A => f (g1 x x))). reflexivity. Qed.
imports: PropExtensionalityFacts