proposition: Corollary exr_fork_assoc {x y z w} (f : x ~> z) (g : y ~> w) (h : x ~> y) : g ∘ exr ∘ (f △ h) ≈ g ∘ h.
proof: Proof. rewrite <- comp_assoc. apply compose_respects; try reflexivity. apply exr_fork. Qed.
imports: Category.Lib Category.Theory.Category Category.Theory.Isomorphism Category.Structure.Terminal