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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]
The ordered pair (a, b) is different from the ordered pair (b, a), unless a = b. In contrast, the unordered pair, denoted {a, b}, always equals the unordered pair {b, a}. Ordered pairs are also called 2-tuples, or sequences (sometimes, lists in a computer science context) of length 2. Ordered pairs of scalars are sometimes called 2-dimensional ...
The axiom of pairing is generally considered uncontroversial, and it or an equivalent appears in just about any axiomatization of set theory. Nevertheless, in the standard formulation of the Zermelo–Fraenkel set theory, the axiom of pairing follows from the axiom schema of replacement applied to any given set with two or more elements, and thus it is sometimes omitted.
2. A Kuratowski ordered pair is a definition of an ordered pair using only set theoretical concepts, specifically, the ordered pair (a, b) is defined as the set {{a}, {a, b}}. 3. "Kuratowski-Zorn lemma" is an alternative name for Zorn's lemma Kurepa 1. Đuro Kurepa 2. The Kurepa hypothesis states that Kurepa trees exist 3.
Otherwise, the unordered pair is called disconnected. A connected graph is an undirected graph in which every unordered pair of vertices in the graph is connected. Otherwise, it is called a disconnected graph. In a directed graph, an ordered pair of vertices (x, y) is called strongly connected if a directed path leads from x to y.
WASHINGTON (Reuters) -U.S. President Donald Trump is considering merging the U.S. Agency for International Development with the State Department to boost its efficiency and ensure its spending is ...
Meet the Montagues and Capulets of condiments.
r : E → {{x,y} : x, y ∈ V}, assigning to each edge an unordered pair of endpoint nodes. Some authors allow multigraphs to have loops, that is, an edge that connects a vertex to itself, [2] while others call these pseudographs, reserving the term multigraph for the case with no loops. [3]