@Nullable
  public static GraphEdge getEdge(@NotNull LinearGraph graph, int up, int down) {
    List<GraphEdge> edges = graph.getAdjacentEdges(up, EdgeFilter.NORMAL_DOWN);
    for (GraphEdge edge : edges) {
      if (intEqual(edge.getDownNodeIndex(), down)) {
        return edge;
      }
    }
    return null;
  }
@Nullable
  public static GraphEdge getEdge(@NotNull LinearGraph graph, int up, int down)