proposition: Lemma shift_less_plus : forall x y z : R, x[-]z [<] y -> x [<] y[+]z.
proof: Proof. intros. rstepl (x[-]z[+]z). apply plus_resp_less_rht. assumption. Qed.
imports: CoRN.tactics.FieldReflection CoRN.tactics.Rational CoRN.algebra.CSetoids Coq(Lia)