proposition: Theorem Qlt_minus : ∀ x y, x < y → 0 < y - x.
proof: Proof. intros x y H. unfold Qlt in H |-*; simpl. rewrite Z.mul_1_r, <- Zopp_mult_distr_l. apply Zlt_left_lt. assumption. Qed.
imports: Utf8 QArith NPeano Sorted Psatz