anchor.diff:    // Graph Interface Methods //
     //-------------------------//
   
  +  /// Returns every [PointNode] that is adjacent to [node].
     List<PointNode> getNeighbors(PointNode node, {bool onlyWalkable: true}) {
       Set<PointNode> neighbors = this._adjacencyMap[node];
       return neighbors.toList();
  
positive.code:     }
    }
  
    List<List<PointNode>> get adjacencyList {
      List<Set<PointNode>> adjacencySet = new List<Set<PointNode>>();
  
  
negative.code: part of path_finding;
  
  /// An undirected graph where each node is tied to a [Point].
  ///
  /// A UndirectedPointGraph can be used for most general
  /// purpose graph needs.
  class UndirectedPointGraph extends Graph {
    Map<PointNode, Set<PointNode>> _adjacencyMap =
      new Map<PointNode, Set<PointNode>>();
  
    /// Default constructor. Use .addAdjacency to populate this [Graph].
    UndirectedPointGraph() {
      
    }
  
    /// Conveinience constructor, that calls .addAdjacency for
    /// each element of [adjacencyList].
    UndirectedPointGraph.fromAdjacencyList(List<List<PointNode>> adjacencyList) {
      if (adjacencyList is! List) {
        throw new ArgumentError('Argument `adjacencyList` must be of type List!');
  