proposition: Lemma sposD x y : lt 0 x -> lt 0 y -> lt 0 (x + y).
proof: Proof. by move=> x_gt0 /andP[_]; apply: sposDl. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun ssrnat eqtype seq choice) mathcomp(div fintype path bigop finset prime order ssralg) mathcomp(poly polydiv mxpoly generic_quotient countalg) mathcomp(ssrnum closed_field ssrint archimedean rat intdiv) mathcomp(algebraics_fundamentals)