Let $L$ be a context-free language, $\bar L$ be its complement and $\bar L_n$ be the length $n$ words in $\bar L_n$.

What is known about $|\bar L_n|$?

Note that it is known that $|L_n|$ is either polynomial (if $L$ is bounded$~$), or grows exponentially. I wonder if anything similar might be true about $|\bar L_n|$. Warning, $L$ is allowed to be ambiguous!


1 Answer 1


From the proof that determining if a CFL ${L}$ = $\Sigma^*$ is undecidable, the set of strings $ID_0\#ID_1^R\#ID_2\#ID_3^R\#\ldots\#ID_t$ where $ID_0,ID_1,\ldots,ID_t$ is a list of the configurations of an accepting nondeterministic TM, is the complement of a context-free language. So $|\overline{L}_n|$ can basically be any computable function less than exponential.


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