(* Algebraic integers. *)
Definition Aint : pred_class :=
fun x : algC => minCpoly x \is a polyOver Cint.
Fact Aint_key : pred_key Aint. Proof. by []. Qed.
Canonical Aint_keyed := KeyedPred Aint_key.

(* This is Isaacs, Corollary (3.5). *)
Corollary Aint_subring : subring_closed Aint.
Canonical Aint_opprPred := OpprPred Aint_subring.