Session-13.pdf - Regular Expression Definition A regular...

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Regular Expression: Definition: A regular expression (sometimes called a rational expression ) is, in theoretical computer science and formal language theory, a sequence of characters that define a search pattern. Usually this pattern is then used by string searching algorithms for "find" or "find and replace" operations on strings. Mathematical Representation: If r and s are regular expressions denoting the languages L(r) and L(s), then Union : (r)|(s) is a regular expression denoting L(r) U L(s) Concatenation : (r)(s) is a regular expression denoting L(r)L(s) Keene closure : (r)* is a regular expression denoting (L(r))* (r) is a regular expression denoting L(r) Regular expressions have the capability to express finite languages by defining a pattern for finite strings of symbols. The grammar defined by regular expressions is known as
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