In graph theory, reachability refers to the ability to get from one vertex to another within a graph. A vertex . In an undirected graph, reachability between all pairs of vertices can be determined by identifying the connected components of the graph.

Reachability is defined as the max value of missing reach to get any subtasks. The usual recursive definition of the reachability of a vertex in a digraph is tight only when the graph is acyclic. There, it is shown that adding reset to the language used in this paper makes even reachability undecidable for programs with at least two arrays.