Noetherian type conjecture for Pixley–Roy hyperspaces

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Let (X,τ)(X,\tau) be a topological space, and let PR(X)=[X]<ωPR(X)=[X]^{<\omega} be the set of finite subsets of XX equipped with the Pixley–Roy topology, whose basic open sets are

[F,U]={G∈PR(X):F⊂G⊂U},[F,U]=\{G\in PR(X):F\subset G\subset U\},

for F∈PR(X)F\in PR(X) and U∈τU\in\tau. Here NtNt denotes the Noetherian type of a topological space. Pixley–Roy hyperspace conjecture.

Nt(PR(X))≤Nt(X).Nt(PR(X))\leq Nt(X).

This conjecture was tested on several examples of spaces. The analogous inequality Nt(Exp⁡(X))≤Nt(X)Nt(\operatorname{Exp}(X))\leq Nt(X) is known for the Vietoris hyperspace of finite subsets, but the authors identify the Pixley–Roy construction as a possible additional exception to the usual computability of cardinal functions.

References

Primary source

Santi Spadaro, “On two topological cardinal invariants of an order-theoretic flavour”, arXiv:1212.5725 (2012).

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