Re: What is the complement of context free language?

Tomasz Kowaltowski <tk@ic.unicamp.br>
Sat, 09 Jun 2007 08:52:08 -0300

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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: Tomasz Kowaltowski <tk@ic.unicamp.br>
Newsgroups: comp.compilers
Date: Sat, 09 Jun 2007 08:52:08 -0300
Organization: IC/UNICAMP
References: 07-06-006
Keywords: theory, parse

> 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?


The complement of a CFL is obviously not only recursively enumerable but
also recursive. Given a CF grammar G, it is easy to imagine a Turing
machine which checks if a given input string belongs to L(G); if so,
reject reject the input, if not, accept it.


-- tk



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