proposition: Lemma fgneg_dom D : {subset dom (fgneg D) <= dom D}.
proof: Proof. by move=> k; rewrite -fgposN => /fgpos_dom; rewrite domN. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)