anchor.diff:  let init p halfDimension max =
       { Bound = { Center = p; HalfDimension = halfDimension};
           Max = max;
  -        Index = 0;
  -        Data = Array.zeroCreate max;
  +        Data = new ConcurrentBag<Point>();
           Node = None }
   
   let createSubQuadTree (q: QuadTree) (dir : Direction) =
  
positive.code:             | x, y -> subdivide q SE
                      |> insert p
  
  
negative.code:     | SW
      | SE
      
  type Node = { NW: QuadTree option; NE: QuadTree option; SE: QuadTree option; SW: QuadTree option }
  and QuadTree = { Bound : Bound; Max : int; Data : ConcurrentBag<Point>; mutable Node : Node option }
  
  let emptyNode = {NW = None; NE = None; SW = None; SE = None }
  
  