The regular expression a*ba* includes strings (or words) such as b, ab, aba, aab, aaba, aabaa . Every regualar expression denotes a set of strings. The regular expression a*ba* represents the following infinite set:

a*ba* = { b, ab, aba, aab, aaba, aabaa, aaabaa, aaabaaa, . . . }

Every string in the above regualr expression must have exactly one b which may be preceded by zero or more a's, and followed by zero or more a's . In a regular expression, a* means "zero or more a's".

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