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  2. Null set - Wikipedia

    en.wikipedia.org/wiki/Null_set

    For example, the set of natural numbers ⁠ ⁠, the set of rational numbers ⁠ ⁠ and the set of algebraic numbers ⁠ ⁠ are all countably infinite and therefore are null sets when considered as subsets of the real numbers. The Cantor set is an example of an uncountable null set. It is uncountable because it contains all numbers between 0 ...

  3. Signed measure - Wikipedia

    en.wikipedia.org/wiki/Signed_measure

    μ(E) ≥ 0 for each E in Σ such that E ⊆ P — in other words, P is a positive set; μ(E) ≤ 0 for each E in Σ such that E ⊆ N — that is, N is a negative set. Moreover, this decomposition is unique up to adding to/subtracting μ-null sets from P and N. Consider then two non-negative measures μ + and μ − defined by

  4. 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.

  5. Set-theoretic definition of natural numbers - Wikipedia

    en.wikipedia.org/wiki/Set-theoretic_definition...

    The set N of natural numbers is defined in this system as the smallest set containing 0 and closed under the successor function S defined by S(n) = n ∪ {n}. The structure N, 0, S is a model of the Peano axioms (Goldrei 1996). The existence of the set N is equivalent to the axiom of infinity in ZF set theory.

  6. Zero element - Wikipedia

    en.wikipedia.org/wiki/Zero_element

    Examples include: The empty set, which is an absorbing element under Cartesian product of sets, since { } × S = { } The zero function or zero map defined by z(x) = 0 under pointwise multiplication (f ⋅ g)(x) = f(x) ⋅ g(x) Many absorbing elements are also additive identities, including the empty set and the zero function.

  7. Initial and terminal objects - Wikipedia

    en.wikipedia.org/wiki/Initial_and_terminal_objects

    The empty set is the unique initial object in Set, the category of sets.Every one-element set is a terminal object in this category; there are no zero objects.. Similarly, the empty space is the unique initial object in Top, the category of topological spaces and every one-point space is a terminal object in thi

  8. Signed zero - Wikipedia

    en.wikipedia.org/wiki/Signed_zero

    Signed zero is zero with an associated sign.In ordinary arithmetic, the number 0 does not have a sign, so that −0, +0 and 0 are equivalent. However, in computing, some number representations allow for the existence of two zeros, often denoted by −0 (negative zero) and +0 (positive zero), regarded as equal by the numerical comparison operations but with possible different behaviors in ...

  9. Semipredicate problem - Wikipedia

    en.wikipedia.org/wiki/Semipredicate_problem

    For example, consider the function index, which takes a string and a substring, and returns the integer index of the substring in the main string. If the search fails, the function may be programmed to return −1 (or any other negative value), since this can never signify a successful result.