proposition: Lemma inl_merge {x z w : C} (f : z ~> x) (g : w ~> x) : f ▽ g ∘ inl ≈ f.
proof: Proof. apply (@exl_fork _ O). Qed.
imports: Category.Lib Category.Theory.Category Category.Theory.Isomorphism Category.Structure.Cartesian Category.Structure.Initial Category.Construction.Opposite