proposition: Lemma ker_coset : 'ker (coset H) = H.
proof: Proof. by rewrite ker_coset_prim genGid (setIidPl _) ?normG. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)