proposition: Lemma ker_trivm (G : {group aT}) : 'ker (trivm G) = G.
proof: Proof. by apply/setIidPl/subsetP=> x _; rewrite !inE /=. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup)