proposition: Lemma lteifBrDl C x y z : (x < y - z ?<= if C) = (z + x < y ?<= if C).
proof: Proof. by case: C; rewrite /= lterBDl. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)