A quantitative variant of the multi-colored Motzkin-Rabin theorem

TL;DR

This paper establishes a quantitative version of the multi-colored Motzkin-Rabin theorem, showing that under certain collinearity conditions, the union of points from multiple sets is confined to a low-dimensional subspace.

Contribution

It provides a new quantitative bound on the dimension of the union of colored point sets satisfying collinearity conditions, extending the classical Motzkin-Rabin theorem.

Findings

Union of point sets lies in a low-dimensional subspace

Dimension bound depends only on number of colors and collinearity parameter

Generalizes the classical Motzkin-Rabin theorem with quantitative estimates

Abstract

We prove a quantitative version of the multi-colored Motzkin-Rabin theorem in the spirit of [BDWY12]: Let $V_1,\ldots,V_n \subset R^d$ be $n$ disjoint sets of points (of $n$ `colors'). Suppose that for every $V_i$ and every point $v \in V_i$ there are at least $\delta |V_i|$ other points $u \in V_i$ so that the line connecting $v$ and $u$ contains a third point of another color. Then the union of the points in all $n$ sets is contained in a subspace of dimension bounded by a function of $n$ and $\delta$ alone.