We study the complexity of the reachability problem for Vector Addition Systems with States (VASSes) in fixed dimensions. We provide four lower bounds improving the currently known state-of-the-art: 1) \np-hardness for unary flat 4-VASSes (VASSes in dimension 4), 2) \pspace-hardness for unary 5-VASSes, 3) \expspace-hardness for binary 6-VASSes and 4) \tower-hardness for unary 8-VASSes.
@article{arxiv.2203.04243,
title = {Lower Bounds for the Reachability Problem in Fixed Dimensional VASSes},
author = {Wojciech Czerwiński and Łukasz Orlikowski},
journal= {arXiv preprint arXiv:2203.04243},
year = {2022}
}