proposition: Lemma Equal_com_arrow_equiv : Equivalence Equal_com_arrow.
proof: Proof. apply Build_Equivalence; unfold Equal_com_arrow in |- *. unfold Reflexive in |- *; intro f. apply Refl. apply Build_Partial_equivalence. unfold Transitive in |- *; intros f g h H1 H2. apply Trans with (Mor_com_arrow g); assumption. unfold Symmetric in |- *; intros f g H. apply Sym; assumption. Qed.
imports: Functor