A combinatorial approach to colourful simplicial depth

TL;DR

This paper proves the colourful simplicial depth conjecture in four dimensions and improves lower bounds in higher dimensions using a combinatorial framework called octahedral systems.

Contribution

It introduces octahedral systems as a combinatorial tool to analyze colourful simplicial depth and verifies the conjecture in dimension four.

Findings

Confirmed the conjecture in dimension 4.

Strengthened lower bounds for higher dimensions.

Identified properties and limitations of octahedral systems.

Abstract

The colourful simplicial depth conjecture states that any point in the convex hull of each of d+1 sets, or colours, of d+1 points in general position in R^d is contained in at least d^2+1 simplices with one vertex from each set. We verify the conjecture in dimension 4 and strengthen the known lower bounds in higher dimensions. These results are obtained using a combinatorial generalization of colourful point configurations called octahedral systems. We present properties of octahedral systems generalizing earlier results on colourful point configurations and exhibit an octahedral system which can not arise from a colourful point configuration. The number of octahedral systems is also given.