Kleene star
Sign in to saveAlso known as Kleene closure, Kleene operator, zero or more, Kleene star operator, 0 or more
unary operation on sets of strings, used in regular expressions for "zero or more repetitions"
~6 min read
Encyclopedic overview
In formal language theory, the Kleene star (or Kleene operator or Kleene closure) refers to two related unary operations, that can be applied either to an alphabet of symbols or to a formal language, a set of strings (finite sequences of symbols).
The Kleene star operator on an alphabet V generates the set V* of all finite-length strings over V, that is, finite sequences whose elements belong to V; in mathematics, it is more commonly known as the free monoid construction. The Kleene star operator on a language L generates another language L*, the set of all strings that can be obtained as a concatenation of zero or more members of L. In both cases, repetitions are allowed.
Excerpted from Wikipedia’s “Kleene star” article, available under the CC BY-SA 4.0 licence.