In mathematical logic and computer science, the Kleene star (or Kleene operator or Kleene closure) is a unary operation, either on sets of strings or on sets of symbols or characters. In mathematics it is more commonly known as the free monoid construction. The application of the Kleene star to a set V is written as V*. It is widely used for regular expressions, which is the context in which it was introduced by Stephen Kleene to characterise certain automata, where it means "zero or more".
- If V is a set of strings then V* is defined as the smallest superset of V that contains λ (the empty string) and is closed under the string concatenation operation.
- If V is a set of symbols or characters then V* is the set of all strings over symbols in V, including the empty string.
The set V* can also be described as the set of finite-length strings that can be generated by concatenating arbitrary elements of V allowing the use of the same element multiple times. If V is a nonempty finite set then V* is a countably infinite set.
The operators are used in rewrite rules for generative grammars.
Read more about Kleene Star: Definition and Notation, Kleene Plus, Examples, Generalization
Famous quotes containing the word star:
“The professional celebrity, male and female, is the crowning result of the star system of a society that makes a fetish of competition. In America, this system is carried to the point where a man who can knock a small white ball into a series of holes in the ground with more efficiency than anyone else thereby gains social access to the President of the United States.”
—C. Wright Mills (19161962)