Let Σ = {a, b}. For a word w ∈ Σ* , let na(x) denote the number of a’s in w and let nb(x) denote the number of b’s in w. Consider the following language: 
L := {xy | x, y ∈ Σ* , na(x) = nb(y)} 
What can we say about L?

(A) L is regular, but not context-free. 

(B) L is context-free, but not regular.

(C) L is Σ*.

(D) None of these.

Hint: 

Responses

More Comments

how can it be ∑* ,if number of a = number of b

sumitverma's picture

@somethingnew Read the below line twice :)
L := {xy | x, y ∈ Σ* , na(x) = nb(y)} 
It is na(x) and nb(y) not na(xy) or nb(xy).

@sumitverma , letw= aab

does w ∈ L

if yes, then how would you decompose it to x and y

sumitverma's picture

@somethingnew
x= a 
y=ab

ok got it, thanx

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