{A A' B B' : Type} (h : A + B -> A' + B') (Ha : forall a:A, is_inl (h (inl a))) (Hb : forall b:B, is_inr (h (inr b))) : functor_sum (unfunctor_sum_l h Ha) (unfunctor_sum_r h Hb) == h. Proof. intros [a|b]; simpl. - unfold unfunctor_sum_l; apply inl_un_inl. - unfold unfunctor_sum_r; apply inr_un_inr. Defined.
Require Import HoTT.Basics. Require Import Types.Empty Types.Unit Types.Prod Types.Sigma. Require Import Types.Bool.