Minimal obstructions for normal spanning trees
Nathan Bowler, Stefan Geschke, Max F. Pitz · Fundamenta Mathematicae · 2018
Diestel and Leader have characterised connected graphs that admit a normal spanning tree via two classes of forbidden minors. One class is Halin’s $(\aleph _0,\aleph _1)$-graphs: bipartite graphs with bipartition $(A,B)$ such that $| A | = \aleph _0$,