proposition: Lemma cent_set1 x : 'C([set x]) = 'C[x].
proof: Proof. by apply: big_pred1 => y /=; rewrite !inE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)