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2. Set (mathematics) - Wikipedia

   en.wikipedia.org/wiki/Set_(mathematics)

   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 ...

3. Class (set theory) - Wikipedia

   en.wikipedia.org/wiki/Class_(set_theory)

   A class that is not a set (informally in Zermelo–Fraenkel) is called a proper class, and a class that is a set is sometimes called a small class. For instance, the class of all ordinal numbers , and the class of all sets, are proper classes in many formal systems.

4. Family of sets - Wikipedia

   en.wikipedia.org/wiki/Family_of_sets

   In set theory and related branches of mathematics, a family (or collection) can mean, depending upon the context, any of the following: set, indexed set, multiset, or class. A collection of subsets of a given set is called a family of subsets of , or a family of sets over .

5. List of set classes - Wikipedia

   en.wikipedia.org/wiki/List_of_set_classes

   The difference between the interval vectors of a set and its complement is <X, X, X, X, X, X/2>, where (in base-ten) X = 12 – 2C, where C is the smaller set's cardinality. In nearly all cases, complements of unsymmetrical sets are related by inversion—i.e., the complement of an "A" version of a set of cardinality C is (usually) the "B ...

6. Pointclass - Wikipedia

   en.wikipedia.org/wiki/Pointclass

   The pointclasses in the Borel hierarchy, and in the more complex projective hierarchy, are represented by sub- and super-scripted Greek letters in boldface fonts; for example, is the pointclass of all closed sets, is the pointclass of all F σ sets, is the collection of all sets that are simultaneously F σ and G δ, and is the pointclass of all analytic sets.

7. Borel set - Wikipedia

   en.wikipedia.org/wiki/Borel_set

   This set is not Borel. However, it is analytic (all Borel sets are also analytic), and complete in the class of analytic sets. For more details see descriptive set theory and the book by A. S. Kechris (see References), especially Exercise (27.2) on page 209, Definition (22.9) on page 169, Exercise (3.4)(ii) on page 14, and on page 196.