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For example, the Euclidean topology on the plane admits as a base the set of all open rectangles with horizontal and vertical sides, and a nonempty intersection of two such basic open sets is also a basic open set. But another base for the same topology is the collection of all open disks; and here the full (B2) condition is necessary.
A three-dimensional model of a figure-eight knot.The figure-eight knot is a prime knot and has an Alexander–Briggs notation of 4 1.. Topology (from the Greek words τόπος, 'place, location', and λόγος, 'study') is the branch of mathematics concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling ...
A base (or basis) B for a topological space X with topology T is a collection of open sets in T such that every open set in T can be written as a union of elements of B. [3] [4] We say that the base generates the topology T. Bases are useful because many properties of topologies can be reduced to statements about a base that generates that ...
Product topology. Restricted product; Quotient space; Unit interval; Continuum (topology) Extended real number line; Long line (topology) Sierpinski space; Cantor set, Cantor space, Cantor cube; Space-filling curve; Topologist's sine curve; Uniform norm; Weak topology; Strong topology; Hilbert cube; Lower limit topology; Sorgenfrey plane; Real ...
Base (topology) – Collection of open sets used to define a topology; Filter (set theory) – Family of sets representing "large" sets; Filters in topology – Use of filters to describe and characterize all basic topological notions and results. Locally convex topological vector space – Vector space with a topology defined by convex open sets
The term topology was introduced by Johann Benedict Listing in the 19th century, although it was not until the first decades of the 20th century that the idea of a topological space was developed. This is a list of topology topics. See also: Topology glossary; List of topologies; List of general topology topics; List of geometric topology topics
A space is pseudocompact if every continuous real-valued function on the space is bounded. σ-compact. A space is σ-compact if it is the union of countably many compact subsets. Lindelöf. A space is Lindelöf if every open cover has a countable subcover. Paracompact. A space is paracompact if every open cover has an open locally finite ...
In mathematics, the support of a real-valued function is the subset of the function domain of elements that are not mapped to zero. If the domain of f {\displaystyle f} is a topological space , then the support of f {\displaystyle f} is instead defined as the smallest closed set containing all points not mapped to zero.