anchor.diff:  module QuadTree
   
  +open System.Collections.Concurrent
  +
   type Point = { Lat :float; Lng : float}
  -type Bound = { Center : Point; HalfDimension :float }
  -
  +type Bound = { Center : Point; HalfDimension : float }
   
   type Direction =
       | NW 
  
positive.code: let init p halfDimension max =
      { Bound = { Center = p; HalfDimension = halfDimension};
          Max = max;
          Index = 0;
          Data = Array.zeroCreate max;
          Node = None }
  
  let createSubQuadTree (q: QuadTree) (dir : Direction) =
  
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 }
  
  