proposition: Lemma modpD d p q : (p + q) %% d = p %% d + q %% d.
proof: Proof. have [-> | dn0] := eqVneq d 0; first by rewrite !modp0. by apply: IdomainUnit.modpD; rewrite unitfE lead_coef_eq0. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop ssralg poly)