public JGraphHierarchyModel run(JGraphFacade facade,
JGraphHierarchyModel model) {
if (model == null) {
Object[] vertices = getOrderedVertices(facade);
// create model using this ordering
model = new JGraphHierarchyModel(facade, vertices, true, false, true);
} else {
// else we're removing the cycles in a currently constructed HM
// TODO
return null;
}