proposition: Lemma dvdp_subr d m n : d %| m -> (d %| m - n) = (d %| n).
proof: Proof. by move=> ?; apply: dvdp_add_eq; rewrite -addrA addNr simp. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop ssralg poly)