Multiplicities of eigenvalues and tree-width of graphs
Journal of Combinatorial Theory Series B
Graphs with magnetic Schrödinger operators of low corank
Journal of Combinatorial Theory Series B
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Let v(G) be the graph invariant introduced by Colin de Verdière in J. Combin. Theory Ser. B. 74 (1998) 121. Let k ≥ 0, and let H be an excluded minor of the class of graphs G with v(G) ≤ k. We show that H has no vertex cuts of size at most two and that, if S is a vertex cut of size three of H, then G - S has two components, and S is the neighbourhood of a vertex v and the subgraph induced by S ∪ {v} is isomorphic to one of the graphs in a certain collection of six graphs.