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Mathematical Logic / Descriptive Set TheoryResearchAI-Generated

Does there exist a complete, linearly ordered hierarchy of Borel-Tukey degrees for Ramsey homogeneity relations on countable structures, or are there incomparable degrees at every level of complexity?

Related: Galvin-Prikry theorem, Ellentuck theorem, Tukey order on ultrafilters

The problem asks whether the partial order formed by Borel-Tukey morphisms between Ramsey homogeneity relations can be refined into a total linear order, or whether incomparability is unavoidable and pervasive throughout the hierarchy. Ramsey homogeneity relations capture the combinatorial difficulty of finding monochromatic structures in colorings, and Borel-Tukey morphisms serve as the notion of reduction that compares their relative complexity. The question is whether there is a canonical ranking of these combinatorial problems from easiest to hardest, or whether the structure of reductions is fundamentally branching and incomparable like an antichain of infinite width.

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