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Kleene star

Kleene star (star closure; Kleene closure; iteration) An operation on formal languages that gives for any language L the language L*, defined by {Λ} ∪ L LL LLL ∪ …

where Λ is the empty word. Thus a word w is in L* if and only if it has the form w1w2wn

with each wi in L, i.e. is a concatenation of words in L.

The Kleene-plus (L+) of L, is defined by LLLLLL ∪ …

Thus L+ comprises the nonempty strings of L*.

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