proposition: Theorem paws_left {x y z : C} (f : x ~> y) : paws ∘ left (z:=z) f ≈ right f ∘ paws.
proof: Proof. symmetry; apply (@swap_second _ O y x z f). Qed.
imports: Category.Lib Category.Theory.Category Category.Theory.Isomorphism Category.Structure.Cartesian Category.Structure.Initial Category.Construction.Opposite