I am looking for the name (definition?) of X in:
A regular expression is X iff it has exactly one possible match.
Examples: <empty regex>,
I would call such a regex constant. Can I use this name? Is there a similar concept?
Additionally, I would say a regex is literal iff it is constant and the single match is equal to the regex itself (f.e.
a but not
NB: I would greatly appreciate some references, because I would like to cite them.