proposition: Theorem paws_fork {x y z : C} (f : y ~> x) (g : z ~> x) : f ▽ g ∘ paws ≈ g ▽ f.
proof: Proof. apply (@swap_fork _ O). Qed.
imports: Category.Lib Category.Theory.Category Category.Theory.Isomorphism Category.Structure.Cartesian Category.Structure.Initial Category.Construction.Opposite