proposition: Lemma conj_subG x A : x \in G -> A \subset G -> A :^ x \subset G.
proof: Proof. by move=> Gx sAG; rewrite -(conjGid Gx) conjSg. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)