fact: Definition baer_sum_inverse_r `{Univalence} {A B : AbGroup} (E : AbSES B A) : abses_baer_sum (abses_pullback (-grp_homo_id) E) E = point (AbSES B A) := baer_sum_commutative _ _ @ baer_sum_inverse_l _.
imports: Basics Types WildCat Pointed.Core AbGroups.AbelianGroup AbGroups.Biproduct AbGroups.AbHom AbSES.Core AbSES.Pullback AbSES.Pushout AbSES.DirectSum Homotopy.HSpace.Core