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  2. Empty set - Wikipedia

    en.wikipedia.org/wiki/Empty_set

    The empty set is the set containing no elements. In mathematics, the empty set or void set is the unique set having no elements; its size or cardinality (count of elements in a set) is zero. [1] Some axiomatic set theories ensure that the empty set exists by including an axiom of empty set, while in other theories, its existence can be deduced.

  3. Von Neumann universe - Wikipedia

    en.wikipedia.org/wiki/Von_Neumann_universe

    Von Neumann universe. In set theory and related branches of mathematics, the von Neumann universe, or von Neumann hierarchy of sets, denoted by V, is the class of hereditary well-founded sets. This collection, which is formalized by Zermelo–Fraenkel set theory (ZFC), is often used to provide an interpretation or motivation of the axioms of ZFC.

  4. Zermelo–Fraenkel set theory - Wikipedia

    en.wikipedia.org/wiki/Zermelo–Fraenkel_set_theory

    Thus the empty set is added at stage 1, and the set containing the empty set is added at stage 2. [11] The collection of all sets that are obtained in this way, over all the stages, is known as V. The sets in V can be arranged into a hierarchy by assigning to each set the first stage at which that set was added to V.

  5. Furstenberg's proof of the infinitude of primes - Wikipedia

    en.wikipedia.org/wiki/Furstenberg's_proof_of_the...

    Since any non-empty open set contains an infinite sequence, a finite non-empty set cannot be open; put another way, the complement of a finite non-empty set cannot be a closed set. The basis sets S(a, b) are both open and closed: they are open by definition, and we can write S(a, b) as the complement of an open set as follows:

  6. Vector space - Wikipedia

    en.wikipedia.org/wiki/Vector_space

    A linear subspace or vector subspace W of a vector space V is a non-empty subset of V that is closed under vector addition and scalar multiplication; that is, the sum of two elements of W and the product of an element of W by a scalar belong to W. [10] This implies that every linear combination of elements of W belongs to W. A linear subspace ...

  7. Axiom of empty set - Wikipedia

    en.wikipedia.org/wiki/Axiom_of_empty_set

    In axiomatic set theory, the axiom of empty set, [1][2] also called the axiom of null set[3] and the axiom of existence, [4][5] is a statement that asserts the existence of a set with no elements. [3] It is an axiom of Kripke–Platek set theory and the variant of general set theory that Burgess (2005) calls "ST," and a demonstrable truth in ...

  8. Examples of vector spaces - Wikipedia

    en.wikipedia.org/wiki/Examples_of_vector_spaces

    Main article: Coordinate space. A basic example of a vector space is the following. For any positive integer n, the set of all n -tuples of elements of F forms an n -dimensional vector space over F sometimes called coordinate space and denoted Fn. [1] An element of Fn is written. where each xi is an element of F.

  9. Event (probability theory) - Wikipedia

    en.wikipedia.org/wiki/Event_(probability_theory)

    v. t. e. In probability theory, an event is a set of outcomes of an experiment (a subset of the sample space) to which a probability is assigned. [1] A single outcome may be an element of many different events, [2] and different events in an experiment are usually not equally likely, since they may include very different groups of outcomes. [3 ...