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The power object of a set A is given by its power set, and the exponential object of the sets A and B is given by the set of all functions from A to B. Set is thus a topos (and in particular cartesian closed and exact in the sense of Barr). Set is not abelian, additive nor preadditive. Every non-empty set is an injective object in Set.
Formally, a function of n variables is a function whose domain is a set of n-tuples. [note 3] For example, multiplication of integers is a function of two variables, or bivariate function, whose domain is the set of all ordered pairs (2-tuples) of integers, and whose codomain is the set of
This article lists mathematical properties and laws of sets, involving the set-theoretic operations of union, intersection, and complementation and the relations of set equality and set inclusion. It also provides systematic procedures for evaluating expressions, and performing calculations, involving these operations and relations.
The intersection A ∩ B is the set of all things that are members of both A and B. Likewise, the intersection is formally defined by the corresponding logical conjunction (). Further, if there are no common elements between A and B, i.e. if the intersection of A and B is the empty set (A ∩ B = ∅), then A and B are said to be disjoint.
The only translation-invariant measure on = with domain ℘ that is finite on every compact subset of is the trivial set function ℘ [,] that is identically equal to (that is, it sends every to ) [6] However, if countable additivity is weakened to finite additivity then a non-trivial set function with these properties does exist and moreover ...
In set theory, X Y is the notation representing the set of all functions from Y to X. As "2" can be defined as {0, 1} (see, for example, von Neumann ordinals), 2 S (i.e., {0, 1} S) is the set of all functions from S to {0, 1}. As shown above, 2 S and the power set of S, P (S), are considered identical set-theoretically.
Given a set A, the identity function on A is a bijection from A to itself, showing that every set A is equinumerous to itself: A ~ A. Symmetry For every bijection between two sets A and B there exists an inverse function which is a bijection between B and A, implying that if a set A is equinumerous to a set B then B is also equinumerous to A: A ...
The algebra of sets is the set-theoretic analogue of the algebra of numbers. Just as arithmetic addition and multiplication are associative and commutative, so are set union and intersection; just as the arithmetic relation "less than or equal" is reflexive, antisymmetric and transitive, so is the set relation of "subset".