@Override
  public @NotNull VisibleGraph<Integer> createVisibleGraph(@NotNull Options options,
                                                           @Nullable Set<? extends Integer> headsOfVisibleBranches,
                                                           @Nullable Set<? extends Integer> filter) {
    return EmptyVisibleGraph.getInstance();
  }
@Override
  public @NotNull VisibleGraph<Integer> createVisibleGraph(@NotNull Options options,
                                                           @Nullable Set<? extends Integer> headsOfVisibleBranches,
                                                           @Nullable Set<? extends Integer> filter)