# Prove/ Disprove: If $L$ is a CFL then $A(L)$ is a CFL too

Consider the operation $A(L)$:

$$A(L) = \{ w: w\in L \land w_R \notin L \}$$

where $w_R$ is the reverse of $w$.

Prove/ Disprove: if $L$ is a CFL language so does $A(L)$.

I am almost certain there's a counter-example but I couldn't find a proper one. I'd be glad for help!

Thanks

• What have you tried? Where did you get stuck? We do not want to just do your exercise for you; we want you to gain understanding. However, as it is we do not know what your underlying problem is, so we can not begin to help. See here for a relevant discussion. If you are uncertain how to improve your question, why not ask around in Computer Science Chat? You may also want to check out our reference questions.
– D.W.
May 18 '15 at 15:33

Consider any language $K \subseteq \{a,b\}^*$, and let $1,2$ be two new symbols. Let $L = 1\cdot \{a,b\}^* \cdot 2 \cup 2 \cdot K \cdot 1$.
What if $1x2\in A(L)$?
Hint: First, try the following. Prove/disprove: if $L$ is regular, then so is $A(L)$.