proposition: Theorem first_split {x y z v u : C} (f : y ~> z) (h : x ~> y) (g : v ~> u) : first f ∘ split h g ≈ split (f ∘ h) g.
proof: Proof. unfork. Qed.
imports: Category.Lib Category.Theory.Category Category.Theory.Isomorphism Category.Structure.Terminal