proposition: Lemma domZ_subset c D : {subset dom (c *: D) <= dom D}.
proof: Proof. move=> x; rewrite !mem_dom coeffZ. by case: (coeff _ _ =P 0)=> // ->; rewrite mulr0 eqxx. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)