{A B A' B'} (f : A -> A') (g : B -> B') `{O_inverts f} `{O_inverts g} : O (A + B) <~> O (A' + B') := Build_Equiv _ _ _ (O_inverts_functor_sum f g).
Require Import HoTT.Basics HoTT.Types. Require Import Equiv.BiInv Extensions HProp HFiber NullHomotopy Limits.Pullback. Require Import Homotopy.IdentitySystems. Require Import Colimits.Pushout.