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Re^2: Why machine-generated solutions will never cease to amaze meby hv (Prior) |
on Nov 11, 2004 at 13:34 UTC ( [id://407031]=note: print w/replies, xml ) | Need Help?? |
The proof for the (x?|y) case follows immediately from regex union being commutative. Regexp union is not commutative when one of the alternates is a leading substring of another: then order becomes important - (E|x) will always match E in preference to x. It is the presence of the outer anchors in the original pattern that disambiguates and thus makes it commutative. Hugo
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