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