Exercise 11:

Regular description for σ(L)\sigma(L) where L={w{a,b}x,y:(w=xay    y=2)}L=\{ w \in \{a,b\}^* \mid \exists x,y: (w=xay\;\wedge\;|y|=2) \}
and σ\sigma is the substitution defined by σ(a)={aa}\sigma(a)=\{aa\}^* and σ(b)={a,aba,bab}\sigma(b)=\{a,aba,bab\}
Give a regular description for the image of the set of words over {a,b}\{a,b\}, with an aa in the third position starting from the end, through the substitution σ\sigma defined by σ(a)={aa}\sigma(a)=\{aa\}^* and σ(b)={a,aba,bab}\sigma(b)=\{a,aba,bab\}.
Authors: Guillem Godoy / Documentation:
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