anchor.diff:                      (AvlTree.Empty, head, stream)
                   | AvlTree.Node (rangeAB : Range<_>, left, right, _) ->
                       let left, head, stream =
  -                        if measurer.Compare (rangeXY.MinValue, rangeAB.MinValue) < 0 then
  +                        if compare rangeXY.MinValue rangeAB.MinValue < 0 then
                               diff' left head stream
                           else
                               left, head, stream
  
positive.code:         ||> fold (fun count _ ->
              count + 1)
  
      /// Extracts the maximum (greatest) value from an AVL tree,
      /// returning the value along with the updated tree.
      let rec extractMax (comparer : IComparer<_>) (tree : AvlTree<'T>) =
  
negative.code:             let minPossibleResultCount =
                  let inputCount = count measurer input
                  let streamCount = count measurer stream
                  GenericMaximum 0 (inputCount - streamCount)
              #endif
  
              let head, stream' = AvlTree.extractMin measurer stream
              let result, _, _ = diff' input (Some head) stream'
  
              #if DEBUG
              let resultCount = count measurer result
  