proposition: Lemma helper2 c : inverse C1 C2 D (functor C1 C2 D c) = c.
proof: Proof. path_functor. exists (path_forall _ _ (helper2_helper c)). abstract (unfold helper2_helper; exp_laws_t). Defined.
imports: Category.Core Functor.Core Functor.Paths Functor.Identity Functor.Composition.Core ExponentialLaws.Law4.Functors ExponentialLaws.Tactics