anchor.diff:  
       //
       // TODO : This could be replaced by 'mkt_bal_l' and 'mkt_bal_r'.
  -    static member Balance (l, r, x) : AvlTree<'T> =
  +    static member Balance (l, r, n) : AvlTree<'T> =
           // Preconditions
           assert (AvlTree.AvlInvariant l)
           assert (AvlTree.AvlInvariant r)
  
positive.code:         | Empty -> true
          | Node (_,_,_,_) -> false
  
      /// Creates a AvlTree whose root node holds the specified value
      /// and the specified left and right subtrees.
      static member inline Create (value, l, r : AvlTree<'T>) =
  
negative.code:         | Some (x, y) ->
              if y < a then
                  // [x, y] and [a, b] are disjoint
                  AvlTree.TryDeleteMin stream
                  ||> diff_helper (a, b) right left
              elif b < x then
                  // [a, b] and [x, y] are disjoint
  