A unified approach to Hindman, Ramsey and van der Waerden spaces

TL;DR

This paper unifies various topological spaces related to combinatorial theorems like Hindman's, Ramsey's, and van der Waerden's, providing general theorems, new constructions, and a combinatorial characterization of their relationships.

Contribution

It introduces a unified framework for different types of convergences and spaces, proves general existence theorems, constructs new examples, and characterizes when certain spaces differ using the Katětov order.

Findings

Unified approach to various convergences and spaces

Construction of new spaces with specific properties

Characterization of space relationships via Katětov order

Abstract

For many years, there have been conducting research (e.g. by Bergelson, Furstenberg, Kojman, Kubi\'{s}, Shelah, Szeptycki, Weiss) into sequentially compact spaces that are, in a sense, topological counterparts of some combinatorial theorems, for instance Ramsey's theorem for coloring graphs, Hindman's finite sums theorem and van der Waerden's arithmetical progressions theorem. These spaces are defined with the aid of different kinds of convergences: IP-convergence, R-convergence and ordinary convergence. The first aim of this paper is to present a unified approach to these various types of convergences and spaces. Then, using this unified approach, we prove some general theorems about existence of the considered spaces and show that all results obtained so far in this subject can be derived from our theorems. The second aim of this paper is to obtain new results about the specific types of these spaces. For instance, we construct a Hausdorff Hindman space that is not an $\I_{1/n}$-space and a Hausdorff differentially compact space that is not Hindman. Moreover, we compare Ramsey spaces with other types of spaces. For instance, we construct a Ramsey space that is not Hindman and a Hindman space that is not Ramsey. The last aim of this paper is to provide a characterization that shows when there exists a space of one considered type that is not of the other kind. This characterization is expressed in purely combinatorial manner with the aid of the so-called Kat\v{e}tov order that has been extensively examined for many years so far. This paper may interest the general audience of mathematicians as the results we obtain are on the intersection of topology, combinatorics, set theory and number theory.