proposition: Lemma osource_twoarrow_nt : forall a u1 v1 u2 v2 r s, osource (twoarrow_nt a u1 v1 u2 v2 r s) = twoarrow_cat.
proof: Proof. ir. uf osource. rw source_twoarrow_nt. rww source_twoarrow_functor. Qed.
imports: Arith cat_examples cardinal fc_limits