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From: ge@hobbit.sci.kun.nl (Ge' Weijers)
Newsgroups: comp.editors
Subject: Re: pattern matches
Summary: inverse of pattern should be possible
Message-ID: <295@hobbit.sci.kun.nl>
Date: 7 Jul 88 11:27:28 GMT
References: <427@grand.UUCP> <37200009@m.cs.uiuc.edu> <18838@cornell.UUCP>
Organization: University of Nijmegen, The Netherlands.
Lines: 16

In article <18838@cornell.UUCP>, blandy@marduk.cs.cornell.edu (Jim Blandy) writes:
> I do think negation is well-defined; using the proposed syntax, (pat)^
> matches any string pat would not.  Since the set of strings matched by
> pat is (presumably) well-defined, the set for (pat)^ is too.
> 
> About the claim that "negation should be trivial, since it only entails
> flipping the accept/reject-ingness of the states in the automaton...":
> 

The complement of a regular expression is a regular expression, although the
derivation is not quite trivial. Matching a (xyz)^ is possible in theory
and in practice. So if someone can whip up some code to generate
the complement.....
-- 
Ge' Weijers, Informatics dept., Nijmegen University, the Netherlands
UUCP: {uunet!,}mcvax!kunivv1!hobbit!ge