proposition: Lemma ltr_pwDr y x z : 0 < x -> y <= z -> y < z + x.
proof: Proof. by move=> *; rewrite addrC ltr_pwDl. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)