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A string is a substring (or factor) [1] of a string if there exists two strings and such that =.In particular, the empty string is a substring of every string. Example: The string = ana is equal to substrings (and subsequences) of = banana at two different offsets:
The empty string has several properties: |ε| = 0. Its string length is zero. ε ⋅ s = s ⋅ ε = s. The empty string is the identity element of the concatenation operation. The set of all strings forms a free monoid with respect to ⋅ and ε. ε R = ε. Reversal of the empty string produces the empty string, so the empty string is a palindrome.
A derivation also imposes in some sense a hierarchical structure on the string that is derived. For example, if the string "1 + 1 + a" is derived according to the leftmost derivation outlined above, the structure of the string would be: {{1} S + {{1} S + {a} S} S} S. where {...} S indicates a substring recognized as belonging to S. This ...
String functions are used in computer programming languages to manipulate a string or query information about a string (some do both).. Most programming languages that have a string datatype will have some string functions although there may be other low-level ways within each language to handle strings directly.
For example, a space character (U+0020 SPACE, ASCII 32) represents blank space such as a word divider in a Western script. A printable character results in output when rendered, but a whitespace character does not. Instead, whitespace characters define the layout of text to a limited degree, interrupting the normal sequence of rendering ...
In JavaScript, the empty string (""), null, undefined, NaN, +0, −0 and false [3] are sometimes called falsy (of which the complement is truthy) to distinguish between strictly type-checked and coerced Booleans (see also: JavaScript syntax#Type conversion). [4] As opposed to Python, empty containers (Arrays, Maps, Sets) are considered truthy.
For example, in Python, raw strings are preceded by an r or R – compare 'C:\\Windows' with r'C:\Windows' (though, a Python raw string cannot end in an odd number of backslashes). Python 2 also distinguishes two types of strings: 8-bit ASCII ("bytes") strings (the default), explicitly indicated with a b or B prefix, and Unicode strings ...
For example, the alphabet {,} with the rules {,}, where is the empty string, is a presentation of the free group on one generator. If instead the rules are just { a b → ε } {\displaystyle \{ab\rightarrow \varepsilon \}} , then we obtain a presentation of the bicyclic monoid .