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  5. 2026

General and Set-Theoretic Topology

Icon: calendar General & ST Session #3.2 | 2026 Mar 12 from 10:55AM to 11:25AM (Central Time (US & Canada)) | Heritage Hall Building 124

‟Higher Lindelöf trees” by Pedro Marun <marun@math.cas.cz>, Czech Academy of Sciences

Abstract:

Given an infinite cardinal $\kappa$ and a $\kappa$-splitting $\kappa^+$-tree $T$, we topologize $T$ as follows: if $x\in T$, then sets of the form $\uparrow x \setminus \uparrow F$, for $F$ a set of immediate successors of $x$ with $ F <\kappa$, form a basis of neighbourhoods of $x$. We then ask whether $T$ is $\kappa^+$-compact with respect to this topology and characterize this property in purely order-theoretic terms. Such trees are necessarily $\kappa^+$-Aronszajn, so they may (consistently) not exist when $\kappa\ge\aleph_1$. In this talk, discuss how to construct such trees using Proxy Principles, introduced by Brodsky and Rinot. We will also mention a further consitency result on the non-existence of such trees together with the failure of the tree property at $\aleph_2$. This is joint work with Ari Meir Brodksy.