Next Tuesday I'll have to orally discuss a test that I did a few days ago with my Theoretical Computer Science professor. In the test, there was an exercise that I couldn't solve that stated:
Specify two non-regular languages $L_2$ and $L_3$ on the alphabet $\{a,b\}$, so that $L_2 \setminus L_3$ is infinite and regular.
I know that regular languages are closed under union, intersection and complement but I just can't figure out how to apply the property in this case.