proposition: Lemma groupJr x y : y \in G -> (x ^ y \in G) = (x \in G).
proof: Proof. by move=> Gy; rewrite groupMl (groupMr, groupV). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)