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  2. Empty string - Wikipedia

    en.wikipedia.org/wiki/Empty_string

    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.

  3. Substring - Wikipedia

    en.wikipedia.org/wiki/Substring

    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:

  4. String (computer science) - Wikipedia

    en.wikipedia.org/wiki/String_(computer_science)

    For example, if Σ = {0, 1}, then 01011 is a string over Σ. The length of a string s is the number of symbols in s (the length of the sequence) and can be any non-negative integer; it is often denoted as |s|. The empty string is the unique string over Σ of length 0, and is denoted ε or λ. [25] [26]

  5. Comparison of programming languages (string functions)

    en.wikipedia.org/wiki/Comparison_of_programming...

    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.

  6. Kleene star - Wikipedia

    en.wikipedia.org/wiki/Kleene_star

    Example of Kleene star applied to the empty set: ∅ * = {ε}. Example of Kleene plus applied to the empty set: ∅ + = ∅ ∅ * = { } = ∅, where concatenation is an associative and noncommutative product. Example of Kleene plus and Kleene star applied to the singleton set containing the empty string:

  7. Python syntax and semantics - Wikipedia

    en.wikipedia.org/wiki/Python_syntax_and_semantics

    Python supports a wide variety of string operations. Strings in Python are immutable, so a string operation such as a substitution of characters, that in other programming languages might alter the string in place, returns a new string in Python. Performance considerations sometimes push for using special techniques in programs that modify ...

  8. Whitespace character - Wikipedia

    en.wikipedia.org/wiki/Whitespace_character

    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 ...

  9. Context-free grammar - Wikipedia

    en.wikipedia.org/wiki/Context-free_grammar

    which defines a string with a different structure {{{1} S + {1} S} S + {a} S} S. and a different parse tree: Note however that both parse trees can be obtained by both leftmost and rightmost derivations. For example, the last tree can be obtained with the leftmost derivation as follows: S → S + S (by rule 1 on the leftmost S)