English

Structure and regularity for subsets of groups with finite VC-dimension

Combinatorics 2022-03-04 v4 Group Theory Logic

Abstract

Suppose GG is a finite group and AGA\subseteq G is such that {gA:gG}\{gA:g\in G\} has VC-dimension strictly less than kk. We find algebraically well-structured sets in GG which, up to a chosen ϵ>0\epsilon>0, describe the structure of AA and behave regularly with respect to translates of AA. For the subclass of groups with uniformly fixed finite exponent rr, these algebraic objects are normal subgroups with index bounded in terms of kk, rr, and ϵ\epsilon. For arbitrary groups, we use Bohr neighborhoods of bounded rank and width inside normal subgroups of bounded index. Our proofs are largely model theoretic, and heavily rely on a structural analysis of compactifications of pseudofinite groups as inverse limits of Lie groups. The introduction of Bohr neighborhoods into the nonabelian setting uses model theoretic methods related to the work of Breuillard, Green, and Tao and Hrushovski on approximate groups, as well as a result of Alekseev, Glebskii, and Gordon on approximate homomorphisms.

Keywords

Cite

@article{arxiv.1802.04246,
  title  = {Structure and regularity for subsets of groups with finite VC-dimension},
  author = {G. Conant and A. Pillay and C. Terry},
  journal= {arXiv preprint arXiv:1802.04246},
  year   = {2022}
}

Comments

34 pages; final version

R2 v1 2026-06-23T00:19:47.665Z