The language L2 is comprised of words with letters denoted w1 to wn, where n >= 3 (i.e. words are 3 letters or more) and the second letter (w2) matches the last letter (wn).
Given that your alphabet consists of only two letters, you have two possible forms:
- The second letter is a 0; so the word will start with either character (represented by Σ), followed by a 0, then an unknown number of other characters (Σ* - the asterisk denotes zero or more), and then the final 0.
- Or the second letter is a 1; so the word will again start with either character (Σ), but then followed by a 1, an unknown number of other characters (Σ*), and the final 1 again.
When you add these two options together and you have: (Σ0Σ*0) + (Σ1Σ*1)