== Let G = (V, E) be a directed graph, where V is a finite set of nodes, and ESV XV be the set of directed) edges (arcs). In particular, we identify a node as the initial node, and a node as the final node. Let r and B be two non-negative integer variables. Further, we decorate each edge with one of the following four instructions: I:=+1; I:=2 - 1; I ==0?; B?; The result is called a decorated graph (we still use G to denote it). The semantics of a decorated graph is straightforward. It executes from the initial node with some non-negative values of B and x (satisfying 0