EntityQ849775· pop 29· linked from 115 articlesKleene starSign in to saveunary operation on sets of strings, used in regular expressions for "zero or more repetitions"Connectionsformal languageEntityunary operationEntityInternational Standard Book NumberEntityQ15777Entitydigital object identifierEntityempty setEntityregular expressionEntityalgebraic structureEntityfinite setEntitymonoidEntitystringEntitycountable setEntitycharacterEntityautomata theoryEntityStephen Cole KleeneEntityidempotenceEntityalphabetEntityJohn Edward HopcroftEntityconcatenationEntityJeffrey David UllmanEntityCategoriesFormal languagesGrammarNatural language processing