Almost EFX in Hypergraphs

We study the existence of envy-free-up-to-any-good (EFX) allocations of indivisible goods among agents with heterogeneous monotone valuations. Christodoulou et al. (2023) introduced the (multi-hyper)graph setting, where agents and goods are represented by vertices and edges of a graph respectively, and only the endpoints of an edge may have non-zero marginal value for it. Our work simplifies and extends previous results of Kaviani et al. (Alireza Kaviani, Masoud Seddighin, Amir Mohammad Shahrezaei. Almost Envy-Free Allocation of Indivisible Goods: A Tale of Two Valuations. WINE 2024) in this domain. First, we provide a simpler construction of EF2X allocation for general monotone valuations in hypergraphs with girth at least 3. We extend our ideas when the multiplicity of each edge is 2 and show that an EF3X allocation always exists for additive valuations. Both results can be constructed in polynomial time. Regarding EFX approximations, we provide a simpler construction for $\frac{\sqrt{2}}{2}$-EFX allocations in hypergraphs of girth at least 3 under subadditive valuations. We push the state-of-the-art by establishing the existence of $\frac{2}{3}$-EFX allocations for additive valuations when the edge multiplicity is 2. Both of the latter results can be constructed in pseudo-polynomial time. By addressing these multi-hypergraph settings, our work contributes to the ongoing effort to resolve the existence of EFX in increasingly general and applicable domains.