proposition: Lemma coset1 : coset H 1 :=: H.
proof: Proof. by rewrite morph1 /= genGid. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)