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I know that if a language $L_1$ and a language $L_2$ are regular, then $L1/L2$ is regular.
When we construct a DFA $M'=(Q, \Sigma, \delta, q_0, F)$, for each state $i$ we can make $i$ the start state (we'll represent is using $L'i$) and if $L'i \cap L_2 \neq 0$ then put $q_i$ in $F'$ in $M'$.
I understand the process of constructing an automaton M if both languages are regular, but what if L1 is regular but L2 is any language? How would I construct an automaton for this?