4. Let L?={a} and L2={b}, list all strings of length 2 that are not from L2* U L1* (if you
think there are no such strings then explain why)
5. Let L?={a} and L2={b}, list all strings of length 3 that are not from L1 L2* (if you
think there are no such strings then explain why)
6. Let L?={ab, ba}, list all strings of length 4 that are not from L?* (if you think there are
no such strings then explain why)