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  2. List of statements independent of ZFC - Wikipedia

    en.wikipedia.org/wiki/List_of_statements...

    MA has a tendency to set most interesting cardinal invariants equal to 2 ℵ 0. A subset X of the real line is a strong measure zero set if to every sequence (ε n) of positive reals there exists a sequence of intervals (I n) which covers X and such that I n has length at most ε n. Borel's conjecture, that every strong measure zero set is ...

  3. Null set - Wikipedia

    en.wikipedia.org/wiki/Null_set

    The Sierpiński triangle is an example of a null set of points in . In mathematical analysis, a null set is a Lebesgue measurable set of real numbers that has measure zero. This can be characterized as a set that can be covered by a countable union of intervals of arbitrarily small total length.

  4. 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.

  5. 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.

  6. 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

  7. Set function - Wikipedia

    en.wikipedia.org/wiki/Set_function

    The Lebesgue measure on is a set function that assigns a non-negative real number to every set of real numbers that belongs to the Lebesgue -algebra. [ 5 ] Its definition begins with the set Intervals ⁡ ( R ) {\displaystyle \operatorname {Intervals} (\mathbb {R} )} of all intervals of real numbers, which is a semialgebra on R . {\displaystyle ...

  8. Subset sum problem - Wikipedia

    en.wikipedia.org/wiki/Subset_sum_problem

    In its most general formulation, there is a multiset of integers and a target-sum , and the question is to decide whether any subset of the integers sum to precisely . [1] The problem is known to be NP-complete. Moreover, some restricted variants of it are NP-complete too, for example: [1]

  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.