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The empty string should not be confused with the empty language ∅, which is a formal language (i.e. a set of strings) that contains no strings, not even the 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
See also: the {} template. The #if function selects one of two alternatives based on the truth value of a test string. {{#if: test string | value if true | value if false}} As explained above, a string is considered true if it contains at least one non-whitespace character. Any string containing only whitespace or no characters at all will be ...
By writing {{if empty|a|b|c}} instead of {{#if:a|a|{{#if:b|b|c}}}}, expression a and b do not have to be repeated and evaluated twice. The template provides a fallback order, similar to a try catch based "It is easier to ask for forgiveness than permission" ( EAFP ) programming style.
String concatenation is an associative, but non-commutative operation. The empty string ε serves as the identity element; for any string s, εs = sε = s. Therefore, the set Σ * and the concatenation operation form a monoid, the free monoid generated by Σ.
In abstract algebra, the free monoid on a set is the monoid whose elements are all the finite sequences (or strings) of zero or more elements from that set, with string concatenation as the monoid operation and with the unique sequence of zero elements, often called the empty string and denoted by ε or λ, as the identity element.
A string is a finite sequence of characters. The empty string is denoted by .The concatenation of two string and is denoted by , or shorter by .Concatenating with the empty string makes no difference: = =.
By default, both the Trash and Spam folders empty automatically to keep your account tidy. These settings are set systemically and can't be changed. • Trash deletion frequency - Trash is deleted after 7 days. • Spam deletion frequency - Spam is deleted after 30 days.
The simplest operation is taking a substring, a snippet of the string taken at a certain offset (called an "index") from the start or end. There are a number of legacy templates offering this but for new code use {{#invoke:String|sub|string|startIndex|endIndex}}. The indices are one-based (meaning the first is number one), inclusive (meaning ...