`{Funext} {A B B' C D D' : AbGroup@{u}} {E : AbSES B A} {F : AbSES D C} (f : B' $-> B) (g : D' $-> D) : AbSESMorphism (abses_direct_sum (abses_pullback f E) (abses_pullback g F)) (abses_direct_sum E F) := functor_abses_directsum (abses_pullback_morphism E f) (abses_pullback_morphism F g).
Require Import Basics Types. Require Import HSet Limits.Pullback. Require Import WildCat Pointed.Core Homotopy.ExactSequence. Require Import Modalities.ReflectiveSubuniverse. Require Import AbGroups.AbelianGroup AbGroups.AbPullback AbGroups.Biproduct. Require Import AbSES.Core AbSES.DirectSum.