A regular expression is a technique for describing languages

A regular expression is a technique for describing languages, sets of sentences over a vocabulary. The language of L() = {} (the language with the null string). Does this mean that the language L(9 | ) = {9, } or just {9}?

Solution

the language L(9 | ) =just {9} because ^ indicates empty string or character.hence the possible words can be {9} or {}