fact: Definition abses_trinary_baer_sum `{Univalence} {A B : AbGroup@{u}} (E F G : AbSES B A) : AbSES B A := abses_pullback ab_triagonal (abses_pushout ab_cotriagonal (abses_direct_sum (abses_direct_sum E F) G)).
imports: Basics Types WildCat Pointed.Core AbGroups.AbelianGroup AbGroups.Biproduct AbGroups.AbHom AbSES.Core AbSES.Pullback AbSES.Pushout AbSES.DirectSum Homotopy.HSpace.Core