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The ordered pair (a, b) is different from the ordered pair (b, a), unless a = b. In contrast, the unordered pair, denoted {a, b}, 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 vectors.
An undirected graph with three vertices and three edges. In one restricted but very common sense of the term, [1] [2] a graph is an ordered pair = (,) comprising: , a set of vertices (also called nodes or points);
For example, the red and green binary relations in the diagram are functions, but the blue and black ones are not. An injection: a function that is injective. For example, the green relation in the diagram is an injection, but the red one is not; the black and the blue relation is not even a function. A surjection: a function that is surjective ...
For example, "is a blood relative of" is a symmetric relation, because x is a blood relative of y if and only if y is a blood relative of x. Antisymmetric for all x, y ∈ X, if xRy and yRx then x = y. For example, ≥ is an antisymmetric relation; so is >, but vacuously (the condition in the definition is always false). [11] Asymmetric
In formal terms, a directed graph is an ordered pair G = (V, A) where [1]. V is a set whose elements are called vertices, nodes, or points;; A is a set of ordered pairs of vertices, called arcs, directed edges (sometimes simply edges with the corresponding set named E instead of A), arrows, or directed lines.
It follows that, two ordered pairs (a,b) and (c,d) are equal if and only if a = c and b = d. Alternatively, an ordered pair can be formally thought of as a set {a,b} with a total order . (The notation ( a , b ) is also used to denote an open interval on the real number line , but the context should make it clear which meaning is intended.
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{(,) < < ()} is the set of pairs of real numbers such that y is greater than 0 and less than f(x), for a given function f. Here the cartesian product R × R {\displaystyle \mathbb {R} \times \mathbb {R} } denotes the set of ordered pairs of real numbers.