On Thu, 1 Feb 2018 01:38:58 +0000
Richard Wordingham via Unicode <unicode@unicode.org> wrote:
> I believe the concurrent star of a language A is (|A|)*, where
>
> |A| = {x ∊ A : {x}* is a regular language}
>
> (The definition works for the trace of fully decomposed Unicode
> character strings under canonical equivalence.)
I misremembered. The notation is (/A/)*, where starter-free x ∊ A is
dealt with by converting x into its maximal substrings all of whose
characters are of the same canonical combining class and putting them
in /A/ in place of x.
> Concurrent star is not a perfect generalisation. If ab = ba, then
> X = {aa, ab, b} has the annoying property that X* is a regular trace
> language, but |X|* is a proper subset of X*. For Unicode, X would be
> a rather unusual regular language.
So this is the other way round. We will get /X/ = {aa, a, b}, so X* is
a proper subset of /X/*.
Richard.
