English

The Henson graphs: colorings and codings

Logic 2026-05-05 v2

Abstract

By recent work of \citet{DobrinenICM} and \citet{Balko7} we know that every finite GG in the Henson graph Hn+1\mathbb{H}_{n+1} (the universal ultrahomogeneous (n+1)(n+1)-clique free graph) has exact finite big Ramsey degree k(G,n)k({G,n}). That is, there is a positive integer k(G,n)k({G,n}) such that for each finite coloring CC of the copies of GG in Hn+1\mathbb{H}_{n+1}, there is H~\tilde{\mathbb{H}}, a substructure of Hn+1\mathbb{H}_{n+1} and isomorphic to Hn+1\mathbb{H}_{n+1}, such that in H~\tilde{\mathbb{H}} at most k(G,n)k({G,n}) colors are used on the copies of GG in H~\tilde{\mathbb{H}}. Moreover, for exactness, for some coloring and all corresponding H~\tilde{\mathbb{H}}, all k(G,n)k({G,n}) colors are needed. The ultimate result here is that if G2|G|\geq 2, then there is a finite computable coloring CC such that, for all such H~\tilde{\mathbb{H}}, we have that H~\tilde{\mathbb{H}} computes (G1)\emptyset^{(|G|-1)} (and hence the halting set).

Keywords

Cite

@article{arxiv.2604.09894,
  title  = {The Henson graphs: colorings and codings},
  author = {Peter Cholak and Natasha Dobrinen and Charlie McCoy},
  journal= {arXiv preprint arXiv:2604.09894},
  year   = {2026}
}

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Minor changes

R2 v1 2026-07-01T12:03:50.646Z