anchor.diff:      static member Filter (predicate : char -> bool, charSet : CharSet) : CharSet =
           // Preconditions
           checkNonNull "charSet" charSet
  -        assert (CharDiet.dietInvariant charSet.Tree)
  +        //assert (CharDiet.dietInvariant charSet.Tree)
  +        //assert (CharDiet.intervalsDisjoint charSet.Tree)
   
           let filteredTree =
               (charSet.Tree, charSet.Tree)
  
positive.code:             minElement tree, maxElement tree
  
      /// Comparison function for DIETs.
      let rec comparison (t1 : CharDiet) (t2 : CharDiet) =
          match t1, t2 with
          | Node (_,_,_,_), Empty -> 1
          | Empty, Empty -> 0
          | Empty, Node (_,_,_,_) -> -1
          | Node (_,_,_,_), Node (_,_,_,_) ->
              let (ix1, iy1), r1 = AvlTree.DeleteMin t1
              let (ix2, iy2), r2 = AvlTree.DeleteMin t2
              let c =
                  match compare ix1 ix2 with
                  | 0 -> compare iy1 iy2
                  | d -> -d
              match c with
              | 0 -> comparison r1 r2
              | c -> c
  
      /// Equality function for DIETs.
      let equal (t1 : CharDiet) (t2 : CharDiet) =
          comparison t1 t2 = 0
  
      /// Returns the number of elements in the set.
      let count (tree : CharDiet) =
          // Preconditions
          assert (dietInvariant tree)
          assert (intervalsDisjoint tree)
  
          // OPTIMIZE : Modify this to use a mutable stack instead of an F# list.
          let rec cardinal_aux acc = function
  
negative.code:     /// Gets the maximum (greatest) value stored in the DIET.
      let maxElement (tree : CharDiet) : char =
          // Preconditions
          //assert (dietInvariant tree)
          //assert (intervalsDisjoint tree)
  
          match tree with
          | Empty ->
  