`{Funext} {B A G : AbGroup} (E : AbSES B A) : IsExact (Tr (-1)) (pconst : pUnit ->* ab_hom B G) (fmap10 (A:=Group^op) ab_hom (projection E) G). Proof. apply isexact_purely_O. rapply isexact_homotopic_i. 2: apply iff_grp_isexact_isembedding. 1: by apply phomotopy_homotopy_hset. exact _. Defined.
Require Import Basics Types WildCat HSet Pointed.Core Pointed.pTrunc Pointed.pEquiv