proposition: Lemma axiom_11 : forall {A B : Type'} (a : sum A B), (@_mk_sum A B (@_dest_sum A B a)) = a.
proof: Proof. intros. unfold _mk_sum. apply _dest_sum_inj. rewrite sym. apply (@ε_spec (sum A B)). exists a. reflexivity. Qed.
imports: Coq.Logic.ClassicalEpsilon ClassicalFacts PropExtensionalityFacts Lia PeanoNat ProofIrrelevance