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If X is any set, then the power set of X (the family of all subsets of X) forms a ring of sets in either sense.. If (X, ≤) is a partially ordered set, then its upper sets (the subsets of X with the additional property that if x belongs to an upper set U and x ≤ y, then y must also belong to U) are closed under both intersections and unions.
For a semi-ring , the set of all finite unions of sets in is the ring generated by : = {: = =,} (One can show that () is equal to the set of all finite disjoint unions of sets in ). A content μ {\displaystyle \mu } defined on a semi-ring S {\displaystyle S} can be extended on the ring generated by S . {\displaystyle S.}
๐-rings can be used instead of ๐-fields (๐-algebras) in the development of measure and integration theory, if one does not wish to require that the universal set be measurable. Every ๐-field is also a ๐-ring, but a ๐-ring need not be a ๐-field.
A ring is a set R equipped with two binary operations [a] + (addition) and ⋅ (multiplication) satisfying the following three sets of axioms, called the ring axioms: [1] [2] [3] R is an abelian group under addition, meaning that: (a + b) + c = a + (b + c) for all a, b, c in R (that is, + is associative). a + b = b + a for all a, b in R (that ...
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 ]
The set of functions from a monoid N to a ring R which are nonzero at only finitely many places can be given the structure of a ring known as R[N], the monoid ring of N with coefficients in R. The addition is defined component-wise, so that if c = a + b , then c n = a n + b n for every n in N .