proposition: Lemma gtrDl x y : (x + y < x) = (y < 0).
proof: Proof. by rewrite -{2}[x]addr0 lterD2. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)