proposition: Lemma target_twoarrow_nt : forall a u1 v1 u2 v2 r s, target (twoarrow_nt a u1 v1 u2 v2 r s) = twoarrow_functor a u2 v2.
proof: Proof. ir. uf twoarrow_nt. rww target_nttyd. Qed.
imports: Arith cat_examples cardinal fc_limits