proposition: Lemma qisomE x : qisom (coset G x) = coset H x.
proof: Proof. case Nx: (x \in 'N(H)); first exact: factmE. by rewrite !coset_default ?eqGH ?morph1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)