proposition: Fact eq_c_d: c ≌ d.
proof: Proof. apply (unique W); [rewrite Wc|rewrite Wd]; apply C_bounds; trivial. Qed.
imports: Coq(Relations Equivalence Morphisms Utf8) Coq(ChoiceFacts ClassicalFacts) Coq.Program(Basics) Coq.Logic(SetoidChoice)