In order to investigate these problems, we need some further definitions. We shall assume that G is a connected graph and that v and w are distinct vertices of G. A vw-disconnecting set of G is a set E of edges of G such that each path from v to w includes an edge of E; note that a vw-disconnecting set is a disconnecting set of G. Similarly, a vw-separating set of G is a set S of vertices, other than v or w, such that each path from v to w passes through a vertex of S. In Fig. 28.1, the sets E1