Difference between revisions of "Discrete topology"

Revision as of 19:13, 1 January 2016

on a set $X$

The topology in which every set is open (and therefore every set is closed). The discrete topology is the largest element in the lattice of all topologies on the given set.

How to Cite This Entry:
Discrete topology. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Discrete_topology&oldid=37240

This article was adapted from an original article by A.A. Mal'tsev (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article

@@ Line 1: / Line 1: @@
 ''on a set $X$''
-The topology in which every set is open (and therefore every set is closed). The discrete topology is the largest element in the lattice of all topologies on the given set. The term  "discrete topology"  is sometimes understood in a somewhat wider sense, viz. as a topology in which intersections of arbitrary numbers of open sets are open. In the case of $T_1$-spaces, both definitions coincide. In this sense, the theory of discrete spaces is equivalent to the theory of partially ordered sets.
+The topology in which every set is open (and therefore every set is closed). The discrete topology is the largest element in the lattice of all topologies on the given set.
-====References====
-<table>
-<TR><TD valign="top">[1]</TD> <TD valign="top">  P.S. Aleksandrov,   "Diskrete Räume"  ''Mat. Sb.'' , '''2'''  (1937)  pp. 501–520 {{ZBL|0018.09105}}</TD></TR>
-</table>
-====Comments====
-The equivalence alluded to above is obtained as follows: If $P$ is a pre-ordered set (cf. [[Pre-order|Pre-order]]), then define $O_x = \{ y \in P : y \le x \}$ for $x \in P$. With the topology generated by the sets $O_x$, $P$ becomes a [[Discrete space|discrete space]].
-If $X$ is a discrete space, put $O_x = \cap \{ O : x \in O, \  O \text{open} \}$ for $x \in X$. Then $y \le x$ if and only if $y \in O_x$, defines a pre-order on $X$.
-These constructions are each others inverses. Moreover, discrete $T_0$-spaces correspond to partial orders and  "real"  discrete spaces correspond to discrete orders.
-This simple idea and variations thereof have proven to be extremely fruitful, see, e.g., [[#References|[a1]]].
-====References====
-<table>
-<TR><TD valign="top">[a1]</TD> <TD valign="top">  G. Gierz,   K.H. Hofmann,   K. Keimel,   J.D. Lawson,   M.V. Mislove,   D.S. Scott,   "A compendium of continuous lattices" , Springer  (1980)</TD></TR>
-</table>
-{{TEX|done}}
 [[Category:General topology]]
-[[Category:Order, lattices, ordered algebraic structures]]

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Difference between revisions of "Discrete topology"

Revision as of 19:13, 1 January 2016