proposition: Lemma val_coset x : x \in 'N(H) -> coset H x :=: H :* x.
proof: Proof. by move=> Nx; rewrite val_coset_prim // genGid. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)