proposition: Lemma morphim_pairg1 (H1 : {set gT1}) : pairg1 @* H1 = setX H1 1.
proof: Proof. by rewrite -imset2_pair imset2_set1r morphimEsub ?subsetT. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)