proposition: Lemma inc_homs_is_mor : forall u, (exists a, exists b, (inc a obs & inc b obs & inc u (homs a b)))-> is_mor from_arrows u.
proof: Proof. ir. nin H. nin H. ee. rw is_mor_from_arrows2. rw inc_morphism_set1. sh x. sh x0. ee; am. Qed.
imports: Arith ordinal nat_trans