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