private void renderEditorArrows() {
    Iterator<AbstractLazyStackPanelHeader> iterator = factModelsPanel.getHeaderIterator();

    while (iterator.hasNext()) {
      AbstractLazyStackPanelHeader widget = (AbstractLazyStackPanelHeader) iterator.next();

      if (widget instanceof FactModelEditor) {
        FactModelEditor editor = (FactModelEditor) widget;

        int index = factModels.indexOf(editor.getFactModel());
        editor.setUpVisible(index != 0);
        editor.setDownVisible(index != (factModels.size() - 1));
      }
    }
  }