countable intersection

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• Countable set — Countable redirects here. For the linguistic concept, see Count noun. Not to be confused with (recursively) enumerable sets. In mathematics, a countable set is a set with the same cardinality (number of elements) as some subset of the set of… …   Wikipedia

• intersection — UK [ˈɪntə(r)ˌsekʃ(ə)n] / US [ˈɪntərˌsekʃ(ə)n] noun [countable] Word forms intersection : singular intersection plural intersections a place where roads, lines etc join or cross each other The school is at the intersection of two main roads …   English dictionary

• Finite intersection property — In general topology, the finite intersection property is a property of a collection of subsets of a set X . A collection has this property if the intersection over any finite subcollection of the collection is nonempty.DefinitionLet X be a set… …   Wikipedia

• T-intersection — UK / US noun [countable] Word forms T intersection : singular T intersection plural T intersections American a T junction …   English dictionary

• T-intersection — UK US noun [countable] [singular T intersection plural T intersections] american a t junction Thesaurus: road and traffic signals and crossingshyponym …   Useful english dictionary

• Glossary of topology — This is a glossary of some terms used in the branch of mathematics known as topology. Although there is no absolute distinction between different areas of topology, the focus here is on general topology. The following definitions are also… …   Wikipedia

• Gδ set — In the mathematical field of topology, a Gδ set, is a subset of a topological space that is a countable intersection of open sets. The notation originated in Germany with G for ( German : area) meaning open set in this case and δ for ( German :… …   Wikipedia

• Meagre set — In the mathematical fields of general topology and descriptive set theory, a meagre set (also called a meager set or a set of first category) is a set that, considered as a subset of a (usually larger) topological space, is in a precise sense… …   Wikipedia

• Borel hierarchy — In mathematical logic, the Borel hierarchy is a stratification of the Borel algebra generated by the open subsets of a Polish space; elements of this algebra are called Borel sets. Each Borel set is assigned a unique countable ordinal number… …   Wikipedia

• Borel set — In mathematics, a Borel set is any set in a topological space that can be formed from open sets (or, equivalently, from closed sets) through the operations of countable union, countable intersection, and relative complement. Borel sets are named… …   Wikipedia

• G-delta space — In mathematics, particularly topology, a G delta; space a space in which closed sets are ‘separated’ from their complements using only countably many open sets. A G delta; space may thus be regarded as a space satisfying a different kind of… …   Wikipedia