Coloring directed hypergraphs

TL;DR

This paper explores coloring properties of directed hypergraphs, proving a conjecture for 3-uniform cases, and shows that certain intersection restrictions guarantee a 2-colorability, advancing hypergraph coloring theory.

Contribution

It proves a conjecture on 2-colorability of directed hypergraphs with intersection restrictions specifically for 3-uniform hypergraphs, extending prior extremal results.

Findings

Proved the conjecture for 3-uniform directed hypergraphs.

Established that avoiding a specific hypergraph structure ensures 2-colorability.

Extended understanding of coloring in directed hypergraphs beyond extremal edge counts.

Abstract

Inspired by earlier results about proper and polychromatic coloring of hypergraphs, we investigate such colorings of directed hypergraphs, that is, hypergraphs in which the vertices of each hyperedge is partitioned into two parts, a tail and a head. We present a conjecture of D. P\'alv\"olgyi and the author, which states that directed hypergraphs with a certain restriction on their pairwise intersections can be colored with two colors. Besides other contributions, our main result is a proof of this conjecture for $3$-uniform directed hypergraphs. This result can be phrased equivalently such that if a $3$-uniform directed hypergraph avoids a certain directed hypergraph with two hyperedges, then it admits a proper $2$-coloring. Previously, only extremal problems regarding the maximum number of edges of directed hypergraphs that avoid a certain hyperedge were studied.