How many languages can a Regular Expression describe is it only one or infinite? I have tried to google it but i haven't found any answer?
I know that a Regular Expression describes a Regular Language?
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$\begingroup$ One language, though there might be infinitely many strings described by a regular expression. $\endgroup$– Rick DeckerMay 12, 2021 at 17:05
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3 Answers
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If you look at the definition of regular expressions (they are usually defined in parallel to the language denoted) you see there is only one language denoted by a given expression. That language could be empty, finite or infinite, but that is another question.
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Every regular expression describes one language --- the language of words matched by the regular expression, or, in other words, the language of words accepted by the finite automaton corresponding to the regular expression.
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A language is described by a regular expression if and only if it is regular.
There are infinitely many regular languages over any fixed alphabet.
answered May 13, 2021 at 5:41