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Given a finite alphabet A of symbols, [6] a generalized regular expression R denotes a possibly infinite set of finite-length strings over the alphabet A, called the language of R, denoted L(R). A generalized regular expression can be one of the following (where a is a symbol of the alphabet A, and R and S are generalized regular expressions ...
Given regular expressions R and S, the following operations over them are defined to produce regular expressions: (concatenation) (RS) denotes the set of strings that can be obtained by concatenating a string accepted by R and a string accepted by S (in that order). For example, let R denote {"ab", "c"} and S denote {"d", "ef"}.
Given a set of strings (also called "positive examples"), the task of regular language induction is to come up with a regular expression that denotes a set containing all of them. As an example, given {1, 10, 100}, a "natural" description could be the regular expression 1⋅0 *, corresponding to the informal characterization "a 1 followed by ...
Therefore, the length of the regular expression representing the language accepted by M is at most 1 / 3 (4 n+1 (6s+7)f - f - 3) symbols, where f denotes the number of final states. This exponential blowup is inevitable, because there exist families of DFAs for which any equivalent regular expression must be of exponential size.
To perform a regex search, use the ordinary search box with the syntax insource:/regex/ or intitle:/regex/. The expression regex denotes a regular expression in MediaWiki-flavored regular expression syntax.
An extended context-free grammar (or regular right part grammar) is one in which the right-hand side of the production rules is allowed to be a regular expression over the grammar's terminals and nonterminals. Extended context-free grammars describe exactly the context-free languages.
Regular expressions are often used to specify patterns that software is then asked to match. Generating an NFA by Thompson's construction, and using an appropriate algorithm to simulate it, it is possible to create pattern-matching software with performance that is O ( m n ) {\displaystyle O(mn)} , where m is the length of the regular ...
Here, is the special regular expression denoting the empty set and ε the special one denoting the empty word; E and F are arbitrary regular expressions. The star height h ( L ) of a regular language L is defined as the minimum star height among all regular expressions representing L .