// @(#)$Id: DirectedGraph.pri,v 1.4 1997/07/25 05:32:39 leavens Exp $
// private or protected members for DirectedGraph
protected:
  struct Arc {Node source; Node target;};
  Set<Arc> the_arcs;
  //@ uses DirectedGraphPrivateTrait;
  //@ depends edges on the_arcs;
  //@ invariant edges\any = toEdges(the_arcs, any);