proposition: Corollary merge_inl_inr {x y : C} : inl ▽ inr ≈ @id C (x + y).
proof: Proof. apply (@fork_exl_exr _ O). Qed.
imports: Category.Lib Category.Theory.Category Category.Theory.Isomorphism Category.Structure.Cartesian Category.Structure.Initial Category.Construction.Opposite