unfold ratSubtract.
rattac.
arithNormalize.
remember (n * x * x0 * x1 * x * x0)%nat as a.
assert (n1 * x0 * x1 * x1 * x * x0 = n1 * x1 * x0 * x1 * x * x0)%nat.
do 5 arithSimplify.
rewrite H.
assert (n2 * x * x1 * x1 * x * x0 = n2 * x1 * x * x1 * x * x0)%nat.
do 5 arithSimplify.
rewrite H0.
remember (n1 * x1 * x0 * x1 * x * x0)%nat as b.
remember (n2 * x1 * x * x1 * x * x0)%nat as c.
omega.
Qed.

(* Specifications: *)
Lemma ratDistance_leRat_both : forall r1 r2 d,
ratSubtract r1 r2 <= d ->
ratSubtract r2 r1 <= d ->
ratDistance r1 r2 <= d.