Reflection-principle classifications for labelled Kruskal's theorem
Reflection-principle classifications for labelled Kruskal's theorem
Let denote the labelled Kruskal theorem for trees labelled by natural numbers, and let denote its restriction to labels below . Write for the relevant -reflection principle, and for the corresponding uniform reflection principle. Here is the base theory of recursive comprehension.
Pakhomov–Freund conjectures. The following two equivalences are conjectured:
and
These proposed classifications aim to determine the proof-theoretic strength of labelled Kruskal's theorem and of its finite-label versions, extending the known classification of unlabelled Kruskal's theorem by Rathjen and Weiermann. The source attributes the first equivalence to F. Pakhomov and the second to A. Freund; no resolution is given here.
Sources & referencesView supporting material
Primary source
Gabriele Buriola and Andreas Weiermann, “Proof-Theoretic Relations between Higman's and Kruskal's theorem, and Independence Results for Tree-like Structures”, arXiv:2511.11297 (2026).
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