Re: What is the complement of context free language?

Mustafa Elsheikh <elsheikhmh@gmail.com>
Sat, 09 Jun 2007 08:28:43 -0700

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Related articles
What is the complement of context free language? lijh_vc@yahoo.com.cn (jianhua li) (2007-06-04)
Re: What is the complement of context free language? bagnara@cs.unipr.it (Roberto Bagnara) (2007-06-09)
Re: What is the complement of context free language? tk@ic.unicamp.br (Tomasz Kowaltowski) (2007-06-09)
Re: What is the complement of context free language? elsheikhmh@gmail.com (Mustafa Elsheikh) (2007-06-09)
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From: Mustafa Elsheikh <elsheikhmh@gmail.com>
Newsgroups: comp.compilers
Date: Sat, 09 Jun 2007 08:28:43 -0700
Organization: Compilers Central
References: 07-06-006
Keywords: parse, theory
Posted-Date: 09 Jun 2007 18:30:48 EDT

On Jun 3, 8:31 pm, jianhua li <lijh...@yahoo.com.cn> wrote:
> In many text books, they say that the complememt of context free
> language us not context free language . But they do not say the
> complemet of CFL is context sensitive language or Recursively
> enumerable language ? So what is the language of the complement of
> context free language?


Complement of CFL could possibly be CFL but not necessarily is.
Complement of CFL is both recursive (R) and recursively enumerable
(RE). Why? All CFLs are both R and RE. R languages are closed under
complement (but RE are not). In that context, complement of CFL is R
which is inherently RE.


-Mustafa

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