proposition: Lemma quotientMidl A : H * A / H = A / H.
proof: Proof. by rewrite [_ /_]morphimMl ?normG //= -!quotientE trivg_quotient mul1g. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)