proposition: Lemma bijective_sym: forall {A B} (f: A -> B) (invf: B -> A), bijective f invf -> bijective invf f.
proof: Proof. intros. destruct H as [?H ?H]. split; intros. - rewrite <- (H0 x), <- (H0 y), H1, H0. reflexivity. - apply H, H0. Qed.
imports: Coq.Relations.Relation_Definitions Coq.Lists.List Coq.Program.Basics