          const e = eit.value;
            if (isAssistant(e.toVertex.node)) {
              asstedges.add(e);
            } else {
              childedges.add(e);
            }
          }
          // first remove all edges from PARENT
          eit = asstedges.iterator;
          while (eit.next()) {
            parent.deleteDestinationEdge(eit.value);
          }
          eit = childedges.iterator;
          while (eit.next()) {
            parent.deleteDestinationEdge(eit.value);
          }
        