# Coverability in 1-VASS with Disequality Tests

## TL;DR

This paper investigates the coverability problem in 1-dimensional VASS with disequality tests, showing it is solvable in polynomial time, extending previous results on reachability in weighted graphs.

## Contribution

It generalizes the control-state reachability problem to include disequality constraints, proving polynomial-time solvability for 1-VASS with these tests.

## Key findings

- Coverability in 1-VASS with disequality tests is in P.
- The problem remains solvable despite exponential shortest paths.
- The work extends known complexity results for VASS reachability.

## Abstract

We study a class of reachability problems in weighted graphs with constraints on the accumulated weight of paths. The problems we study can equivalently be formulated in the model of vector addition systems with states (VASS). We consider a version of the vertex-to-vertex reachability problem in which the accumulated weight of a path is required always to be non-negative. This is equivalent to the so-called control-state reachability problem (also called the coverability problem) for 1-dimensional VASS. We show that this problem lies in NC: the class of problems solvable in polylogarithmic parallel time. In our main result we generalise the problem to allow disequality constraints on edges (i.e., we allow edges to be disabled if the accumulated weight is equal to a specific value). We show that in this case the vertex-to-vertex reachability problem is solvable in polynomial time even though a shortest path may have exponential length. In the language of VASS this means that control-state reachability is in polynomial time for 1-dimensional VASS with disequality tests.