Hi. I was wondering if you could help me solve this. I've tried drawing it but it doesn't work, and anyway, I want to be able to solve it in a more elegant manner.

$\displaystyle \bigcap_{m=1}^{+ \infty} \bigcup_{n=1}^{+ \infty} (-\frac {m}{n}, \frac {n}{m})$

Thank you.