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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.
For every set X, there is a unique function, called the empty function, or empty map, from the empty set to X. The graph of an empty function is the empty set. [note 5] The existence of empty functions is needed both for the coherency of the theory and for avoiding exceptions concerning the empty set in many statements.
A set of polygons in an Euler diagram This set equals the one depicted above since both have the very same elements.. In mathematics, a set is a collection of different [1] things; [2] [3] [4] these things are called elements or members of the set and are typically mathematical objects of any kind: numbers, symbols, points in space, lines, other geometrical shapes, variables, or even other ...
We write f: a → b, and we say "f is a morphism from a to b". We write hom(a, b) (or hom C (a, b) when there may be confusion about to which category hom(a, b) refers) to denote the hom-class of all morphisms from a to b. [2] Some authors write the composite of morphisms in "diagrammatic order", writing f;g or fg instead of g ∘ f.
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.
More generally, a collection of any sets whatsoever is called a family of sets, set family, or a set system. Additionally, a family of sets may be defined as a function from a set I {\displaystyle I} , known as the index set, to F {\displaystyle F} , in which case the sets of the family are indexed by members of I {\displaystyle I} . [ 1 ]
A bijective function from a set to itself is also called a permutation, [1] and the set of all permutations of a set forms its symmetric group. Some bijections with further properties have received specific names, which include automorphisms, isomorphisms, homeomorphisms, diffeomorphisms, permutation groups, and most geometric transformations.
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 ...