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Tag Archives: cycle structure
The rational world and the rational Urysohn space
The set Q of rational numbers is obviously an interesting topological space. In 1920, Waclaw Sierpiński gave a lovely characterisation of it. The simplest way to state it is to say that a countable, metrisable, space without isolated points is … Continue reading
Posted in exposition, open problems
Tagged cycle structure, Sierpinski's theorem, Urysohn space
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