To simplify the expression (1/m - n - 1/m + n) / (2/3m - 3n), we first need to combine like terms in the numerator and denominator.

In the numerator:
1/m - 1/m = 0
-n + n = 0

So the numerator simplifies to 0.

In the denominator:
We can rewrite 2/3m as 2/(3m)

Now we can rewrite the expression:

0 / (2/(3m) - 3n)

This simplifies to 0 / (2/(3m) - 3n)

Since the numerator is 0, the final answer is 0.