From: Hans Aberg (haberg@math.su.se)
Date: Sat Oct 13 2007 - 09:07:16 CDT
On 10 Oct 2007, at 19:38, Mark Davis wrote:
> Andy and I put together a paper of recommendations for the UTC at
> http://docs.google.com/Doc?id=dfqr8rd5_32kv97tx .
I suspect you will run into problems when mixing complement with the
Kleene closure (zero or more concatenations) operator (and other
operators generating an infinite number of strings in the associated
language).
So one safe way is to admit the usual set operations on character
classes only, and letting regular expressions having only the usual
operators acting on character classes.
If you don't use such infinite generating operators, the restriction
forms a graded algebra, and it seems me you want the complement with
respect to the grading (length of strings) in the generated language.
Hans Åberg
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