proposition: Lemma subr_le0 x y : (y - x <= 0) = (y <= x).
proof: Proof. by rewrite -[LHS]subr_ge0 opprB add0r subr_ge0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)