> Tim> re1 in re2
>
> Tim> should be True iff the language accepted by re1 is a subset of
> Tim> the language accepted by re2. In this case, it's OK to consider
> Tim> the empty language a subset of all others, since nobody will be
> Tim> able to make head or tail out of the code anyway.
[ark@research.att.com]
> 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.
Sure, that's why I said "empty language" and not "empty string". It
wouldn't make *any* sense for "re1 in re2" to consider a regexp that
accepted the language {""} to be "in" all other regexps. But a regexp that
accepts the language {} (i.e., the empty language) clearly accepts a subset
of the language accepted by any regexp.
> Pedantically y'rs --ark
Not enough to matter in this case <wink>.
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