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E103

[0MP]Difficulty:*.We restrict the topology described in the previous example to the set \(Y=[0,1]^{[0,1]}\) (that is, we restrict \(ℝ\) to \([0,1]\), and set \(Ω=[0,1]\)). Find a sequence \((f_ n)⊂ Y\) that does not allow a convergent subsequence.

Solution 1

[0MQ]

Let’s recall the definition [0J3]: a space \(X\) is ”compact by coverings” if, for every \((A_ i)_{i∈ I}\) family of open such that \(⋃_{i∈ I}A_ i= X\), there is a finite subfamily \(J⊂ I\) such that \(⋃_{i∈ J}A_ i= X\). The Tychonoff theorem shows that this space \(Y\) is ”compact by coverings”. This exercise shows you instead that \(Y\) it is not ”compact by sequences”.

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Bibliography
Book index
  • space, topological
  • topological space
  • subsequence, converging
  • convergence, pointwise ---
  • theorem, Tychonoff —
  • Tychonoff
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