proposition: Lemma class_transl x y z : x \in y ^: G -> (x \in z ^: G) = (y \in z ^: G).
proof: Proof. by rewrite -!(class_sym z) => /class_eqP->. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)