AskDefine | Define subset

Dictionary Definition

subset n : a set whose members are members of another set; a set contained within another set

User Contributed Dictionary

English

Pronunciation

Noun

subset (plural subsets)
  1. Of a given set, a set all the elements of which are in the given set.
    The set of integers is a subset of the set of reals.
  2. A group of things or people, all of which are in a specified larger group.
    We asked a subset of the population of the town for their opinion.

Translations

mathematics: of a set
group contained in a larger group

Derived terms

See also

Extensive Definition

In mathematics, especially in set theory, a set A is a subset of a set B if A is "contained" inside B. Notice that A and B may coincide. The relationship of one set being a subset of another is called inclusion.

Definitions

If A and B are sets and every element of A is also an element of B, then:
  • A is a subset of (or is included in) B, denoted by A \subseteq B,
or equivalently
  • B is a superset of (or includes) A, denoted by B \supseteq A.
If A is a subset of B, but A is not equal to B (i.e. there exists at least one element of B not contained in A), then
  • A is also a proper (or strict) subset of B; this is written as A\subsetneq B.
or equivalently
  • B is a proper superset of A; this is written as B\supsetneq A.
For any set S, the inclusion relation ⊆ is a partial order on the set 2S of all subsets of S (the power set of S).

The symbols ⊂ and ⊃

Other authors prefer to use the symbols ⊂ and ⊃ to indicate proper subset and superset, respectively, in place of \subsetneq and \supsetneq. This usage makes ⊆ and ⊂ analogous to ≤ and < For example, if x ≤ y then x may be equal to y, or maybe not, but if x < y, then x definitely does not equal y, but is strictly less than y. Similarly, using the "⊂ means proper subset" convention, if A ⊆ B, then A may or may not be equal to B, but if A ⊂ B, then A is definitely not equal to B.

Examples

  • The set is a proper subset of .
  • Any set is a subset of itself, but not a proper subset.
  • The empty set, written , is also a subset of any given set X. (This statement is vacuously true, see proof below) The empty set is always a proper subset, except of itself.
  • The set is a proper subset of
  • The set of natural numbers is a proper subset of the set of rational numbers and the set of points in a line segment is a proper subset of the set of points in a line. These are counter-intuitive examples in which both the part and the whole are infinite, and the part has the same number of elements as the whole (see Cardinality of infinite sets).

Other properties of inclusion

Inclusion is the canonical partial order in the sense that every partially ordered set (X, \preceq) is isomorphic to some collection of sets ordered by inclusion. The ordinal numbers are a simple example—if each ordinal n is identified with the set [n] of all ordinals less than or equal to n, then a ≤ b if and only if [a] ⊆ [b].
For the power set 2S of a set S, the inclusion partial order is (up to an order isomorphism) the Cartesian product of k = |S| (the cardinality of S) copies of the partial order on for which 0 < 1. This can be illustrated by enumerating S = and associating with each subset T ⊆ S (which is to say with each element of 2S) the k-tuple from k of which the ith coordinate is 1 if and only if si is a member of T.
subset in Bengali: উপসেট
subset in Belarusian (Tarashkevitsa): Падмноства
subset in Catalan: Subconjunt
subset in Czech: Podmnožina
subset in German: Teilmenge
subset in Estonian: Alamhulk
subset in Modern Greek (1453-): Υποσύνολο
subset in Spanish: Subconjunto
subset in Esperanto: Subaro
subset in Persian: زیرمجموعه
subset in French: Sous-ensemble
subset in Classical Chinese: 子集
subset in Korean: 부분집합
subset in Icelandic: Hlutmengi
subset in Italian: Sottoinsieme
subset in Hebrew: תת קבוצה
subset in Hungarian: Részhalmaz
subset in Dutch: Deelverzameling
subset in Japanese: 部分集合
subset in Norwegian: Delmengde
subset in Polish: Podzbiór
subset in Portuguese: Subconjunto
subset in Russian: Подмножество
subset in Simple English: Subset
subset in Slovak: Podmnožina
subset in Slovenian: Podmnožica
subset in Serbian: Подскуп
subset in Finnish: Osajoukko
subset in Swedish: Delmängd
subset in Ukrainian: Підмножина
subset in Võro: Alambhulk
subset in Chinese: 子集
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