proposition: Lemma memJ_conjg A x y : (y ^ x \in A :^ x) = (y \in A).
proof: Proof. by rewrite mem_conjg conjgK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)