proposition: Lemma dvdp_add_eq d m n : d %| m + n -> (d %| m) = (d %| n).
proof: Proof. by move=> ?; apply/idP/idP; [move/dvdp_addr <-| move/dvdp_addl <-]. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop ssralg poly)