>> Note the distinction between the empty language and the empty
>> string. As a language is a set of strings, the empty language is
>> one that contains no strings, not even the empty string.
>> Therefore, a regular expression that accepts the empty language is
>> one that rejects every string, even the empty string.
Tim> Sure, that's why I said "empty language" and not "empty string".
Tim> It wouldn't make *any* sense for "re1 in re2" to consider a
Tim> regexp that accepted the language {""} to be "in" all other
Tim> regexps. But a regexp that accepts the language {} (i.e., the
Tim> empty language) clearly accepts a subset of the language accepted
Tim> by any regexp.
Right. (I wasn't disagreeing with you, merely pointing out a
plausible miscomprehension on the part of the reader (because
I made just that mistake the first time I read it))
>> Pedantically y'rs --ark
Tim> Not enough to matter in this case <wink>.
Whether it matters depends on whether the reader made the same
mistake I did on first reading.
--
Andrew Koenig, ark@research.att.com, http://www.research.att.com/info/ark
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