proposition: Lemma norm_rlcoset G x : x \in 'N(G) -> G :* x = x *: G.
proof: Proof. by rewrite -sub1set => /normC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)