English

Distality Rank

Logic 2021-10-26 v2

Abstract

Building on Pierre Simon's notion of distality, we introduce distality rank as a property of first-order theories and give examples for each rank mm such that 1mω1\leq m \leq \omega. For NIP theories, we show that distality rank is invariant under base change. We also define a generalization of type orthogonality called mm-determinacy and show that theories of distality rank mm require certain products to be mm-determined. Furthermore, for NIP theories, this behavior characterizes mm-distality. If we narrow the scope to stable theories, we observe that mm-distality can be characterized by the maximum cycle size found in the forking "geometry," so it coincides with (m1)(m-1)-triviality. On a broader scale, we see that mm-distality is a strengthening of Saharon Shelah's notion of mm-dependence.

Keywords

Cite

@article{arxiv.1908.11400,
  title  = {Distality Rank},
  author = {Roland Walker},
  journal= {arXiv preprint arXiv:1908.11400},
  year   = {2021}
}

Comments

32 pages

R2 v1 2026-06-23T11:00:18.783Z