A topological space that is neither discrete nor indiscrete

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SUMMARY

A topological space can exist that is neither discrete nor indiscrete while having every set in the topology be clopen. The example discussed involves the space X = {0, 1, 2, 3} with open sets ∅, {0, 1}, {2, 3}, and X itself. In this configuration, each open set is also closed, confirming the clopen property. This is distinct from the ordinary topology on R, which does not support such a structure.

PREREQUISITES
  • Understanding of basic topology concepts, including open and closed sets.
  • Familiarity with clopen sets in topological spaces.
  • Knowledge of discrete and indiscrete topologies.
  • Basic set theory, particularly regarding unions and intersections of sets.
NEXT STEPS
  • Study the properties of clopen sets in various topological spaces.
  • Explore examples of non-discrete and non-indiscrete topologies.
  • Learn about the implications of open and closed sets in topological structures.
  • Investigate the relationship between topology and set theory in more depth.
USEFUL FOR

Mathematicians, students of topology, and anyone interested in advanced set theory concepts will benefit from this discussion.

DotKite
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Homework Statement



is it possible to have a topological space that is neither the indiscrete nor the discrete, and very set in the topology is clopen?

Homework Equations





The Attempt at a Solution



let ##X## = {(0,1),(2,3)} with the ordinary topology on R.
(0,1) is open, but it's complement which is (2,3) is open and which means (0,1) is closed. This (0,1) is clopen. Same argument for (2,3). Is this right?
 
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DotKite said:

Homework Statement



is it possible to have a topological space that is neither the indiscrete nor the discrete, and very set in the topology is clopen?

Homework Equations


The Attempt at a Solution



let ##X## = {(0,1),(2,3)} with the ordinary topology on R.
(0,1) is open, but it's complement which is (2,3) is open and which means (0,1) is closed. This (0,1) is clopen. Same argument for (2,3). Is this right?

Yes, it is. But you aren't stating it very well. Your space is ##X##={0,1,2,3}. Your open sets are ∅,{0,1},{2,3},X. Then every open set is also closed, as you say. And that is NOT the ordinary topology on R.
 

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