proposition: Lemma cent1C x y : (x \in 'C[y]) = (y \in 'C[x]).
proof: Proof. by rewrite !cent1E eq_sym. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)