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| -rw-r--r-- | txr.1 | 4 |
1 files changed, 2 insertions, 2 deletions
@@ -2889,9 +2889,9 @@ that they are of some use. .SS Equivalence to Sets Regexp intersection is not essential; it may be obtained from complement and -union as follows, since DeMorgan's law applies to regular expression algebra: +union as follows, since De Morgan's law applies to regular expression algebra: (R1)&(R2) = ~(~(R1)|~(R2)). (The complement of the union of the complements of -R1 and R2 constitutes the intersection. This law works because the regular +R1 and R2 constitutes the intersection.) This law works because the regular expression operators denote set operations in a straightforward way. A regular expression denotes a set of strings (a potentially infinite one) in a condensed way. The union of two regular expressions R1 | R2 denotes the union of the set |