Namespaces
Variants
Actions

Difference between revisions of "Discrete topology"

From Encyclopedia of Mathematics
Jump to: navigation, search
m (→‎Comments: better)
(→‎References: isbn link)
 
(4 intermediate revisions by one other user not shown)
Line 1: Line 1:
 
''on a set $X$''
 
''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.  If $X$ is a space with the discrete topology, then every map from $X$ to any other topological space is continuous.
  
 
====References====
 
====References====
−
<table>
+
* J.L. Kelley, "General topology", Graduate Texts in Mathematics '''27''' Springer (1975) {{ISBN|0-387-90125-6}} {{MR|0370454}} {{ZBL|0306.54002}}
−
<TR><TD valign="top">[1]</TD> <TD valign="top">  P.S. Aleksandrov,   "Diskrete Räume" ''Mat. Sb.'' , '''2''' (1937) pp. 501–520</TD></TR>
 
−
</table>
 
  
−
 
+
[[Category:General topology]]
−
 
 
−
====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}}
 

Latest revision as of 18:49, 14 November 2023

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. If $X$ is a space with the discrete topology, then every map from $X$ to any other topological space is continuous.

References

  • J.L. Kelley, "General topology", Graduate Texts in Mathematics 27 Springer (1975) ISBN 0-387-90125-6 MR0370454 Zbl 0306.54002
How to Cite This Entry:
Discrete topology. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Discrete_topology&oldid=34128
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
Retrieved from "https://encyclopediaofmath.org/index.php?title=Discrete_topology&oldid=54457"