Given $L_1,L_2$ which can be any regular / non-regular languages.
Let $L_1$ and $L_1-L_2$ be regular languages.
I want to know if $L_1\cap L_2$ must be regular or not.
So, I wrote $L_1-L_2=L_1\cap L_2^c$ which is regular.
From here I don't really know what to do, because $L_2^c$ can be wither regular or non-regular.
I think that I struggle to understand what the difference operations actually means.