Χώρος Hausdorff
- Ένας Μαθηματικός Χώρος.
Ετυμολογία[]
Η ονομασία "Χώρος Hausdorff" σχετίζεται ετυμολογικά με το όνομα του μαθηματικού "Hausdorff".
Hausdorff spaces are named after Felix Hausdorff, one of the founders of topology. Hausdorff's original definition of a topological space (in 1914) included the Hausdorff condition as an axiom.
Ορισμός[]
A Hausdorff space is a topological space with a separation property:
any two distinct points can be separated by disjoint open sets
(that is,
whenever p and q are distinct points of a set X,
there exist disjoint open sets Up and Uq such that
Up contains p and Uq contains q.
Εισαγωγή[]
In topology and related branches of mathematics, a Hausdorff space, separated space or T2 space is a topological space in which distinct points have disjoint neighbourhoods.
Of the many separation axioms that can be imposed on a topological space, the "Hausdorff condition" (T2) is the most frequently used and discussed.
It implies the uniqueness of limits of sequences, nets, and filters.
Definitions[]
Points x and y in a topological space X can be separated by neighbourhoods if there exists a neighbourhood U of x and a neighbourhood V of y such that U and V are disjoint (U ∩ V = ∅). X is a Hausdorff space if all distinct points in X are pairwise neighborhood-separable.
This condition is the third separation axiom (after T0 and T1), which is why Hausdorff spaces are also called T2 spaces. The name separated space is also used.
A related, but weaker, notion is that of a preregular space. X is a preregular space if any two topologically distinguishable points can be separated by neighbourhoods. Preregular spaces are also called R1 spaces.
The relationship between these two conditions is as follows. A topological space is Hausdorff if and only if it is both preregular (i.e. topologically distinguishable points are separated by neighbourhoods) and Kolmogorov (i.e. distinct points are topologically distinguishable). A topological space is preregular if and only if its Kolmogorov quotient is Hausdorff.
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