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In the mathematical field of set theory, the continuum means the real numbers, or the corresponding (infinite) cardinal number, denoted by . [ 1 ] [ 2 ] Georg Cantor proved that the cardinality c {\displaystyle {\mathfrak {c}}} is larger than the smallest infinity, namely, ℵ 0 {\displaystyle \aleph _{0}} .
Linear continuum, any ordered set that shares certain properties of the real line; Continuum (topology), a nonempty compact connected metric space (sometimes a Hausdorff space) Continuum hypothesis, a conjecture of Georg Cantor that there is no cardinal number between that of countably infinite sets and the cardinality of the set of all real ...
Set theory is the branch of mathematical logic that studies sets, which can be informally described as collections of objects.Although objects of any kind can be collected into a set, set theory – as a branch of mathematics – is mostly concerned with those that are relevant to mathematics as a whole.
Examples include the class of all groups, the class of all vector spaces, and many others. In category theory, a category whose collection of objects forms a proper class (or whose collection of morphisms forms a proper class) is called a large category. The surreal numbers are a proper class of objects that have the properties of a field.
The simple present, present simple or present indefinite is one of the verb forms associated with the present tense in modern English. It is commonly referred to as a tense, although it also encodes certain information about aspect in addition to the present time. The simple present is the most commonly used verb form in English, accounting for ...
In fact, the cardinality of ℘ (), by definition , is equal to . This can be shown by providing one-to-one mappings in both directions between subsets of a countably infinite set and real numbers, and applying the Cantor–Bernstein–Schroeder theorem according to which two sets with one-to-one mappings in both directions have the same ...
Each choice of definition for 'open set' is called a topology. A set with a topology is called a topological space. Metric spaces are an important class of topological spaces where a real, non-negative distance, also called a metric, can be defined on pairs of points in the set. Having a metric simplifies many proofs, and many of the most ...
A number of multi-word constructions exist to express the combinations of present tense with the basic form of the present tense is called the simple present; there are also constructions known as the present progressive (or present continuous) (e.g. am writing), the present perfect (e.g. have written), and the present perfect progressive (e.g ...