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  2. Open set - Wikipedia

    en.wikipedia.org/wiki/Open_set

    [6] This potentially introduces new open sets: if V is open in the original topology on X, but isn't open in the original topology on X, then is open in the subspace topology on Y. As a concrete example of this, if U is defined as the set of rational numbers in the interval ( 0 , 1 ) , {\displaystyle (0,1),} then U is an open subset of the ...

  3. Base (topology) - Wikipedia

    en.wikipedia.org/wiki/Base_(topology)

    The Zariski topology on the spectrum of a ring has a base consisting of open sets that have specific useful properties. For the usual base for this topology, every finite intersection of basic open sets is a basic open set. The Zariski topology of is the topology that has the algebraic sets as closed sets

  4. General topology - Wikipedia

    en.wikipedia.org/wiki/General_topology

    In the usual topology on R n the basic open sets are the open balls. Similarly, C, the set of complex numbers, and C n have a standard topology in which the basic open sets are open balls. The real line can also be given the lower limit topology. Here, the basic open sets are the half open intervals [a, b).

  5. Topology - Wikipedia

    en.wikipedia.org/wiki/Topology

    The basic object of study is topological spaces, which are sets equipped with a topology, that is, a family of subsets, called open sets, which is closed under finite intersections and (finite or infinite) unions. The fundamental concepts of topology, such as continuity, compactness, and connectedness, can be defined in terms of open sets ...

  6. Open and closed maps - Wikipedia

    en.wikipedia.org/wiki/Open_and_closed_maps

    In mathematics, more specifically in topology, an open map is a function between two topological spaces that maps open sets to open sets. [1] [2] [3] That is, a function : is open if for any open set in , the image is open in . Likewise, a closed map is a function that maps closed sets to closed sets.

  7. Clopen set - Wikipedia

    en.wikipedia.org/wiki/Clopen_set

    In topology, a clopen set (a portmanteau of closed-open set) in a topological space is a set which is both open and closed. That this is possible may seem counterintuitive, as the common meanings of open and closed are antonyms, but their mathematical definitions are not mutually exclusive .

  8. Regular open set - Wikipedia

    en.wikipedia.org/wiki/Regular_open_set

    The interior of a closed subset of is a regular open subset of and likewise, the closure of an open subset of is a regular closed subset of . [2] The intersection (but not necessarily the union) of two regular open sets is a regular open set. Similarly, the union (but not necessarily the intersection) of two regular closed sets is a regular ...

  9. List of general topology topics - Wikipedia

    en.wikipedia.org/wiki/List_of_general_topology...

    1 Basic concepts. 2 Limits. ... Open set, closed set. Clopen set; Closure (topology) ... Compact-open topology; Zariski topology; Kuratowski closure axioms;