annitaz Posted March 1, 2010 Share Posted March 1, 2010 Which one of the following is an example of two sets S and T of strings such that S ⊄ T and T ⊄ S, but S* = T*? 1. S = {a, b, abb, bba} and T = {a, b, bba} 2. S = {a, aaaa} and T = {a, aaa, aaaa} 3. S = {a, ab, aab} and T = {a, ab, abab} 4. S = {a, b, aaa} and T = {a, bbb} 5. S = {bb, bbbb} and T = {b} I have excluded answers 1,2,5 but I am stuck with 3 and 4. When is S* equal to T*? Link to comment Share on other sites More sharing options...
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