If $L1$ is regular language and $L2$ is unknown language then what can we say about $L1-L2$. Will it be regular or not?
I think it will be regular because even if $L2$ is not regular then still (Regular - not Regular) will result in Regular, according to the properties of set.
Because subtracting elements that are not elements of a set from The given set will not change the set.
I want to know if I am right and if I am not then what's the error?