proposition: Lemma gcdp_modl m n : gcdp (m %% n) n %= gcdp m n.
proof: Proof. have [/modp_small -> // | lenm] := ltnP (size m) (size n). by rewrite (gcdpE m n) ltnNge lenm. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop ssralg poly)