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An unordered pair is a finite set; its cardinality (number of elements) is 2 or (if the two elements are not distinct) 1. In axiomatic set theory, the existence of unordered pairs is required by an axiom, the axiom of pairing. More generally, an unordered n-tuple is a set of the form {a 1, a 2,... a n}. [5] [6] [7]
Example of a web form with name-value pairs. A name–value pair, also called an attribute–value pair, key–value pair, or field–value pair, is a fundamental data representation in computing systems and applications. Designers often desire an open-ended data structure that allows for future extension without modifying existing code or data.
HTML tags most commonly come in pairs like < h1 > and </ h1 >, although some represent empty elements and so are unpaired, for example < img >. The first tag in such a pair is the start tag , and the second is the end tag (they are also called opening tags and closing tags ).
In the second example above, the numbering resets after the blank line. This problem is less noticeable with other list types, but it still affects the underlying HTML code and may have disruptive effects for some readers; see WP:LISTGAP for details. In order to be a list, each line must begin the same way. This holds true for mixed lists.
6. Cantor's absolute is a somewhat unclear concept sometimes used to mean the class of all sets 7. Cantor's theorem states that the powerset operation increases cardinalities Card The cardinality of a set Cartesian product The set of all ordered pairs obtained from two sets, where each pair consists of one element from each set. cardinal 1.
Theorem: If A and B are sets, then there is a set A×B which consists of all ordered pairs (a, b) of elements a of A and b of B. Proof: The singleton set with member a, written {a}, is the same as the unordered pair {a, a}, by the axiom of extensionality. The singleton, the set {a, b}, and then also the ordered pair
In one case, A is empty, and in another B is empty, so 2 n − 2 ordered pairs of subsets remain. Finally, since we want unordered pairs rather than ordered pairs we divide this last number by 2, giving the result above. Another explicit expansion of the recurrence-relation gives identities in the spirit of the above example.
Array, a sequence of elements of the same type stored contiguously in memory; Record (also called a structure or struct), a collection of fields . Product type (also called a tuple), a record in which the fields are not named