anchor.diff:      /// Returns the number of elements in the set.
       let count (tree : CharDiet) =
           // Preconditions
  -        assert (AvlTree.AvlInvariant tree)
  +        assert (dietInvariant tree)
   
           // OPTIMIZE : Modify this to use a mutable stack instead of an F# list.
           let rec cardinal_aux acc = function
  
positive.code:     /// Computes the intersection of the two sets.
      let rec intersect (input : CharDiet) (stream : CharDiet) : CharDiet =
          // Preconditions
          assert (AvlTree.AvlInvariant input)
          assert (AvlTree.AvlInvariant stream)
  
          match input, stream with
          | Empty, _
  
negative.code:     /// Gets the maximum (greatest) value stored in the DIET.
      let maxElement (tree : CharDiet) : char =
          // Preconditions
          assert (dietInvariant tree)
  
          match tree with
          | Empty ->
  