Exercise 1:

Context-free description for {w{a,b}wa=wb    wabba>0}\{ w \in \{a,b\}^* \mid |w|_a=|w|_b\;\wedge\;|w|_{abba}>0 \}
Give a context-free description for the set of words over {a,b}\{a,b\} with the same number of aa’s as number of bb’s, and with at least one occurrence of abbaabba.
Authors: Guillem Godoy / Documentation:
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