# On the structure of large sum-free sets of integers

## TL;DR

This paper characterizes the structure of large sum-free subsets of integers, establishes a stability version of Hu's theorem, and confirms a conjecture on the number of partitions into two sum-free sets.

## Contribution

It provides a structural characterization of large sum-free sets, a stability version of Hu's theorem, and confirms a conjecture on the count of such partitions.

## Key findings

- Structural description of sum-free sets with density ≥ 2/5 - c
- A stability version of Hu's theorem for maximum union size
- Number of subsets partitionable into two sum-free sets is Θ(2^{4n/5})

## Abstract

A set of integers is called sum-free if it contains no triple $(x,y,z)$ of not necessarily distinct elements with $x+y=z$. In this paper, we provide a structural characterisation of sum-free subsets of $\{1,2,\ldots,n\}$ of density at least $2/5-c$, where $c$ is an absolute positive constant. As an application, we derive a stability version of Hu's Theorem [Proc. Amer. Math. Soc. 80 (1980), 711-712] about the maximum size of a union of two sum-free sets in $\{1,2,\ldots,n\}$. We then use this result to show that the number of subsets of $\{1,2,\ldots,n\}$ which can be partitioned into two sum-free sets is $\Theta(2^{4n/5})$, confirming a conjecture of Hancock, Staden and Treglown [arXiv:1701.04754].