proposition: Lemma domN D : dom (-D) =i dom D.
proof: Proof. by move=> z; rewrite !mem_dom coeffN oppr_eq0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)