proposition: Lemma contr_equiv A B (f : A -> B) `{IsEquiv A B f} `{Contr A} : Contr B.
proof: Proof. exists (f (center A)). intro y. eapply moveR_E. apply contr. Qed.
imports: Unicode.Utf8 Coq.Program.Tactics Setoid Relations Equations.Type.All CRelationClasses CMorphisms