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arxiv: 1709.10042 · v3 · pith:PAKW33MNnew · submitted 2017-09-28 · 🧮 math.CO

A counterexample regarding labelled well-quasi-ordering

classification 🧮 math.CO
keywords inducedwell-quasi-orderedcounterexampledefinedfinitelyforbiddengraphshereditary
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Korpelainen, Lozin, and Razgon conjectured that a hereditary property of graphs which is well-quasi-ordered by the induced subgraph order and defined by only finitely many minimal forbidden induced subgraphs is labelled well-quasi-ordered, a notion stronger than that of $n$-well-quasi-order introduced by Pouzet in the 1970s. We present a counterexample to this conjecture. In fact, we exhibit a hereditary property of graphs which is well-quasi-ordered by the induced subgraph order and defined by finitely many minimal forbidden induced subgraphs yet is not $2$-well-quasi-ordered. This counterexample is based on the widdershins spiral, which has received some study in the area of permutation patterns.

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