proposition: Corollary from_adj_counit {x y} (f : x ~> U y) : ⌈f⌉ ≈ ε ∘ fmap[F] f.
proof: Proof. rewrite <- (id_left f). rewrite from_adj_nat_l. rewrite fmap_comp; cat. Qed.
imports: Category.Lib Category.Theory.Category Category.Theory.Morphisms Category.Theory.Isomorphism Category.Theory.Functor Category.Instance.Sets