code: public void addEdge(N a, N b)
      {
          if( !containsBoth(a, b) )
              return;//Cant add nodes to things that doing exist
          nodes.get(a).getOutgoing().add(b);
          nodes.get(b).getIncoming().add(a);
      }
docs: Adds a directed edge into the network from <tt>a</tt> to <tt>b</tt>.
  If <tt>a</tt> and <tt>b</tt> are not nodes in the graph, nothing occurs.
  @param a the parent node
  @param b the child node