proposition: Theorem proof_irrelevance_cc : b1 = b2.
proof: Proof. refine (or_elim _ _ _ _ _ (em (b1 = b2))); intro H. - trivial. - apply (NoRetractFromSmallPropositionToProp.paradox B p2b b2p (p2p2 H) p2p1). Qed.
imports: PropExtensionalityFacts Hurkens