End Proof_irrelevance_Prop_Ext_CC.
(** Remark: [prop_extensionality] can be replaced in lemma [ext_prop_dep_proof_irrel_gen] by the weakest property [provable_prop_extensionality]. *)
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(** ** CIC |- prop. ext. -> proof-irrelevance                   *)
(** In the Calculus of Inductive Constructions, inductively defined booleans enjoy dependent case analysis, hence directly proof-irrelevance from propositional extensionality. *)
Section Proof_irrelevance_CIC.
Inductive boolP : Prop :=
| trueP : boolP
| falseP : boolP.
Definition boolP_elim_redl (C:Prop) (c1 c2:C) :
c1 = boolP_ind C c1 c2 trueP := eq_refl c1.
Definition boolP_elim_redr (C:Prop) (c1 c2:C) :
c2 = boolP_ind C c1 c2 falseP := eq_refl c2.
Scheme boolP_indd := Induction for boolP Sort Prop.

Lemma ext_prop_dep_proof_irrel_cic : prop_extensionality -> proof_irrelevance.
End Proof_irrelevance_CIC.