English

On products of elementarily indivisible structures

Logic 2019-09-04 v2 Combinatorics

Abstract

We say a structure MM in a first-order language is indivisible if for every coloring of its universe in two colors, there is a monochromatic substructure MM' of MM such that MM' is isomorphic to MM. Additionally, we say that MM is symmetrically indivisible if MM' can be chosen to be symmetrically embedded in MM (that is, every automorphism of MM' can be extended to an automorphism of MM). Similarly, we say that MM is elementarily indivisible if MM' can be chosen to be an elementary substructure. We define new products of structures in a relational language. We use these products to give recipes for construction of elementarily indivisible structures which are not transitive and elementarily indivisible structures which are not symmetrically indivisible, answering two questions presented by A. Hasson, M. Kojman and A. Onshuus.

Keywords

Cite

@article{arxiv.1502.00897,
  title  = {On products of elementarily indivisible structures},
  author = {Nadav Meir},
  journal= {arXiv preprint arXiv:1502.00897},
  year   = {2019}
}

Comments

21 pages, minor corrections

R2 v1 2026-06-22T08:20:41.836Z