proposition: Lemma uncurry_exl_fork_exr {x y : C} : uncurry exl △ uncurry exr ≈ split eval eval ∘ @doppel (y ^ x) (y ^ x) x.
proof: Proof. unfold doppel. rewrite split_fork. now rewrite !eval_first. Qed.
imports: Category.Lib Category.Theory.Category Category.Theory.Isomorphism Category.Theory.Functor Category.Functor.Bifunctor Category.Structure.Terminal Category.Structure.Cartesian Category.Structure.Monoidal Category.Structure.Monoidal.Internal.Product Category.Structure.Cartesian.Closed Category.Instance.Sets