// This is where we start -- what is the minimal set of operations
// we'd like to perform on a graph?
public interface GraphInterface
{
  public void addVertex(Vertex v);
  public void addEdge(Vertex a, Vertex b);
  public int getNumVertices();
  public int getNumEdges();
  public boolean edgeExists(Vertex a, Vertex b);
  public int degree(Vertex o);
}