# Triangle-degrees in graphs and tetrahedron coverings in 3-graphs

## TL;DR

This paper studies minimum degree conditions in 3-uniform hypergraphs that guarantee every vertex is contained in a specific small hypergraph, providing asymptotic results for triangles and tetrahedra, and relates the problem to graph triangle coverage.

## Contribution

It determines asymptotic bounds for covering vertices with triangles and tetrahedra in 3-graphs, and connects these hypergraph problems to a graph triangle coverage conjecture.

## Key findings

- Asymptotic determination of $c_1(n,F)$ for the generalized triangle $K_4^{(3)-}$.
- Near-optimal bounds for the tetrahedron $K_4^{(3)}$ case.
- Conjectured tight bounds for the maximum number of triangles containing a vertex in dense graphs.

## Abstract

We investigate a covering problem in $3$-uniform hypergraphs ($3$-graphs): given a $3$-graph $F$, what is $c_1(n,F)$, the least integer $d$ such that if $G$ is an $n$-vertex $3$-graph with minimum vertex degree $\delta_1(G)>d$ then every vertex of $G$ is contained in a copy of $F$ in $G$ ? We asymptotically determine $c_1(n,F)$ when $F$ is the generalised triangle $K_4^{(3)-}$, and we give close to optimal bounds in the case where $F$ is the tetrahedron $K_4^{(3)}$ (the complete $3$-graph on $4$ vertices). This latter problem turns out to be a special instance of the following problem for graphs: given an $n$-vertex graph $G$ with $m> n^2/4$ edges, what is the largest $t$ such that some vertex in $G$ must be contained in $t$ triangles? We give upper bound constructions for this problem that we conjecture are asymptotically tight. We prove our conjecture for tripartite graphs, and use flag algebra computations to give some evidence of its truth in the general case.