proposition: Lemma mem_conjg A x y : (y \in A :^ x) = (y ^ x^-1 \in A).
proof: Proof. by rewrite conjg_preim inE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)