Find a topological space which does not have a countable basis

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SUMMARY

The discussion focuses on identifying a topological space that lacks a countable basis. Participants explore various strategies, including considering Cantor-like sets and manipulating familiar spaces such as the real numbers, \(\mathbb{R}\). The key takeaway is that by enlarging the underlying set or increasing the number of open sets beyond the standard topology, one can construct a space that meets the criteria. The challenge lies in ensuring that the resulting topology does not allow for a countable basis.

PREREQUISITES
  • Understanding of topological spaces and their properties
  • Familiarity with the definition of a basis in topology
  • Knowledge of Cantor sets and their characteristics
  • Concept of open sets in different topologies
NEXT STEPS
  • Research the concept of uncountable bases in topology
  • Explore the properties of the Sorgenfrey line as an example of a topology with an uncountable basis
  • Investigate the construction of topologies on \(\mathbb{R}\) with varying numbers of open sets
  • Study the implications of the axiom of choice in relation to bases of topological spaces
USEFUL FOR

Mathematicians, particularly those specializing in topology, students tackling advanced topology problems, and educators seeking examples of topological spaces with uncountable bases.

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Homework Statement


Find a topological space which does not have a countable basis.


Homework Equations


Definition of basis : A collection of subsets which satisfy:
(i) union of every set equals the whole set
(ii) any element from an intersection of two subsets is contained in another subset which is itself contained in the intersection


The Attempt at a Solution


I thought I had it nailed, but the solution i came up with was actually an uncountable basis for the standard euclidean topology, which can also have countable bases. So i need to think of a space which cannot have a countable basis.

I started thinking about a space of cantor-like numbers (infinite strings of 1's and 0's) but this is still a subset of the reals! I am stuck please any hints would be a blessing.
 
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You have complete freedom to choose both the set and the topology you give it. So one strategy you could try is to make your underlying set very large -- say, a large number of copies of some familiar space. Alternatively you could try starting with a familiar set like \mathbb{R}, but giving it very many open sets, many more than the standard topology has.
 

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