Oh, forgot other question regarding regular expressions

Perhaps this is connected with my misunderstanding that has lead to my
earlier post but with regular expressions in the Sipser book definition
1.52 states:

that R is a regular expression if R is:
....
2. "empty"
....

then on the next page is states:

"R[upperscript +] = RR*."

then later

"R[upperscript +] union "empty" = R*

My question is why is R[upperscript +] not already have "empty" in it?
Even though it must have 1 or more concatenations of R doesn't R have
empty in it? And so can't R concat R be potentially "empty" concat
"empty"?

Thanks once again,

Nic

.

Relevant Pages

  • Re: Oh, forgot other question regarding regular expressions
    ... earlier post but with regular expressions in the Sipser book definition ... Even though it must have 1 or more concatenations of R doesn't R have empty in it? ... And so can't R concat R be potentially "empty" concat ...
    (comp.theory)
  • Re: Regular Expressions Problem
    ... Oriana wrote: ... > I'm trying to 'clean up' this source file using regular expressions ... why not just have a flag ... that states you've seen a empty line, and then if the flag is true, do not ...
    (comp.lang.python)
  • Multiple substr() exchange
    ... Using regular expressions or split is inpossible, ... empty elements!!! ... Maybe any CPAN modules??? ... Prev by Date: ...
    (comp.lang.perl.misc)
  • Regular expressions
    ... I need some regular expressions but don't know how to create them. ... If somebody knows a good, easy to use, readable tool. ... (some lines may be left empty) ... Prev by Date: ...
    (microsoft.public.dotnet.framework.aspnet)
  • Re: Regular expressions
    ... Here 2 nice resources that can help: ... > I need some regular expressions but don't know how to create them. ... (some lines may be left empty) ... Prev by Date: ...
    (microsoft.public.dotnet.framework.aspnet)