Kleene star

Summary

The Kleene star $L^*$ of a formal language $L$ is the set of all concatenations of finitely many strings of $L$. It includes the empty string, the concatenation of no strings. Applied to an alphabet $\Sigma$, it gives the set $\Sigma^*$ of all strings. It is one of the three operations, with union and concatenation, that build the regular expressions. It is the basic way to express repetition in formal languages.