There are exactly \omega_1 topological types of locally finite trees with countably many rays

Jorge Bruno, P. Szeptycki

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Abstract

Nash-Williams showed that the collection of locally finite trees under the topological minor relation results in a well-quasi-order. As a consequence, Matthiesen proved that the number λ of topological types of locally finite tree must be uncountable. Since ℵ1≤λ≤c, finding the exact value of λ becomes non-trivial in the absence of the Continuum Hypothesis. In this paper we address this task by showing that λ=ℵ1 for locally finite trees with countably many rays. We also partially extend this result to locally finite trees with uncountably many rays.
Original languageEnglish
Pages (from-to)243-259
Number of pages17
JournalFundamenta Mathematicae
Volume256
Issue number3
DOIs
Publication statusPublished - 6 Oct 2021

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