A simple existence criterion for normal spanning trees in infinite graphs
Abstract
Halin proved in 1978 that there exists a normal spanning tree in every connected graph G that satisfies the following two conditions: (i) G contains no subdivision of a `fat' K_0, one in which every edge has been replaced by uncountably many parallel edges; and (ii) G has no K_0 subgraph. We show that the second condition is unnecessary.
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