![]() This defines the abstract syntax of regular expressions to be contrasted with Given an alphabet Σ the regular expressions are defined by the following BNF Thompson) Regular Expressions: Abstract Syntax Very convenient for representing pattern in documents (K. “algebraic”: expressions with equations such as E 1 +E 2 = E 2 +E 1 E(E 1 +Įach regular expression E represents also a language L(E) They form an “algebraic” representation of ǫ-NFA Regular expressions can be seen as a system of notations for denoting ǫ-NFA
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