@Override
    protected @NotNull RMNode<FoldRegionImpl> createNewNode(@NotNull FoldRegionImpl key,
                                                            int start,
                                                            int end,
                                                            boolean greedyToLeft,
                                                            boolean greedyToRight,
                                                            boolean stickingToRight,
                                                            int layer) {
      return new FRNode(this, key, start, end);
    }
@Override
    protected @NotNull RMNode<FoldRegionImpl> createNewNode(@NotNull FoldRegionImpl key,
                                                            int start,
                                                            int end,
                                                            boolean greedyToLeft,
                                                            boolean greedyToRight,
                                                            boolean stickingToRight,
                                                            int layer)