proposition: Lemma flip_le_minus_l (x y z : R) : y - x ≤ z <-> y ≤ z + x.
proof: Proof. pattern x at 2;apply (transport _ (negate_involutive x)). split; apply flip_le_minus_r. Qed.
imports: HoTT.Classes.interfaces.abstract_algebra HoTT.Classes.interfaces.orders HoTT.Classes.theory.groups HoTT.Classes.theory.rings HoTT.Classes.orders.semirings