Abstract
In this short note we confirm the deep structural correspondence between the complexity of a countable scattered chain (\(=\) strict linear order) and its big Ramsey combinatorics: we show that a countable scattered chain has finite big Ramsey degrees if and only if it is of finite Hausdorff rank. This also provides a complete characterization of countable chains whose big Ramsey spectra are finite. We expand the notion of big Ramsey spectrum to monomorphic structures and give a sufficient condition for a monomorphic countable structure to have finite big Ramsey spectrum.
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Funding
The first author was supported by the http://www.fields.utoronto.ca/ Fields Institute for Research in Mathematical Sciences.The second author was supported by the Science Fund of the Republic of Serbia, Grant No. 7750027: Set-theoretic, model-theoretic and Ramsey-theoretic phenomena in mathematical structures: similarity and diversity – SMART.
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Keegan Dasilva Barbosa and Rajko Nenadov have contributed equally to this work.
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Barbosa, K.D., Mašulović, D. & Nenadov, R. A short note on the characterization of countable chains with finite big Ramsey spectra. Order (2023). https://doi.org/10.1007/s11083-023-09647-5
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DOI: https://doi.org/10.1007/s11083-023-09647-5