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Star height problem - Definition and Overview |
| Related Words: Aggravation, Annoyance, Anxiety, Basis, Bore, Bug, Bugbear, Burden, Case, Catch, Catechism |
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The star-height problem in formal language theory is the question whether all regular languages can be expressed using regular expressions with a limited nesting depth of Kleene stars. Specifically, is a nesting depth of more than 2 required? If so, can we determine how many are required?
This theoretical problem remained open for 25 years until it was solved by Kosaburo Hashiguchi. The answer to all questions is yes: Hashiguchi published an algorithm to determine an expression's star height in 1988.
Also see generalized star height problem.
References
- Kosaburo Hashiguchi, Regular languages of star height one, Information and Control, 53: 199-210, 1982
- Kosaburo Hashiguchi, Algorithms for Determining Relative Star Height and Star Height, Inf. Comput. 78(2): 124-169, 1988
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Example Usage of problem |
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BuzzEdition: Have no clue what the problem is, but I agree! ~~~ RT @ButtercupD: @usnoozin a shot of vodka might help ;) |
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ishiaaa: @iammytch hey i got your text but i have no load haha sure mytch no problem :) We'll just see you in MOA! |
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Danisidhe: @branli Not a problem during the week but makes it difficult to engage with hubby on weekends! |
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