proposition: Corollary merge_comp {x y z w : C} (f : y ~> z) (h : w ~> z) (g : z ~> x) : (g ∘ f) ▽ (g ∘ h) ≈ g ∘ f ▽ h.
proof: Proof. apply (@fork_comp _ O). Qed.
imports: Category.Lib Category.Theory.Category Category.Theory.Isomorphism Category.Structure.Cartesian Category.Structure.Initial Category.Construction.Opposite