anchor.diff:  
   namespace Nu
   open System
  +open System.Collections
   open System.Collections.Generic
   open System.Numerics
   open Prime
  
positive.code: [<RequireQualifiedAccess>]
  module SpatialTree =
  
      /// A spatial structure that organizes elements on a 2D plane.
      /// TODO: document this.
      type [<NoEquality; NoComparison>] SpatialTree<'e when 'e : equality> =
          private
              { Node : 'e SpatialNode
  
negative.code:     let getElementsAtPoint point tree =
          let set = HashSet HashIdentity.Structural
          SpatialNode.getElementsAtPoint point tree.Node set
          new SpatialTreeEnumerable<'e> (new SpatialTreeEnumerator<'e> (tree.OmnipresentElements, set)) :> 'e IEnumerable
  
      let getElementsInBounds bounds tree =
          let set = HashSet HashIdentity.Structural
          SpatialNode.getElementsInBounds bounds tree.Node set
          new SpatialTreeEnumerable<'e> (new SpatialTreeEnumerator<'e> (tree.OmnipresentElements, set)) :> 'e IEnumerable
  
      let getDepth tree =
          SpatialNode.getDepth tree.Node
  