Given two regex patterns R1 and R2, is it possible at all to determine/calculate:
- whether R1 is "a subset of" R2, i.e. all strings that match R1 will also always match R2, but not necessarily the other way around;
- whether R1 is "equivalent" or "equal" to R2, i.e. all strings that match R1 will also always match R2, and all strings that match R2 will also always match R1.
- whether R1 does not "intersect" R2, i.e. no string can match both R1 and R2 at the same time, a string can match either R1 or R2 but never both.
Hm, after browsing a bit, I found this:
http://www.mail-archive.com/[EMAIL PROTECTED]/msg00233.html
Come to think of it, the difficulty of the problem is comparable to determining whether two computer programs are equivalent to each other (i.e. given the same input, it will always generate the same output).
Oh well...
-- dave
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