GraphEdgeEnumeration f = bb.outEdges();
OPT_SpaceEffGraphNode.GraphEdgeEnumeration f = bb.outEdges();
  private void clearBackEdges(OPT_SpaceEffGraphNode bb) {    GraphEdgeEnumeration f = bb.outEdges();    while (f.hasMoreElements()) {      OPT_SpaceEffGraphEdge outEdge = f.next();      outEdge.clearBackEdge();    }  }