# Languages that are not subset, but are union

Are there examples of regular languages $L_1$ and $L_2$, where $L_1$ and $L_2$ is not a subset of each other but that $(L_1 \cup L_2)^* = L_1^* \cup L_2^*$ ?

Yes. Let $L_1=\{a\}, L_2=\{\epsilon\}$. Obviously both languages are regular and neither is a subset of the other. We then have $$(L_1\cup L_2)^*=(a+\epsilon)^*=a^*$$ and since $$L_1^*=a^*,\quad L_2^*=\epsilon^*=\epsilon$$ we have $$L_1^*\cup L_2^*=a^*\cup \epsilon = a^*$$
• More generally, any two regular languages where $L_2 \subseteq L_1^*$ and which aren't subsets of each other will do. – G. Bach Dec 1 '15 at 21:15