anchor.diff:      /// Returns the number of elements in the set.
       let count (tree : CharDiet) =
           // Preconditions
  -        //assert (dietInvariant tree)
  -        //assert (fst <| intervalsDisjoint tree Set.empty)
  +        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
  
positive.code:     //
      let rec internal (*private*) find_del_left p (tree : CharDiet) : char * CharDiet =
          // Preconditions
          //assert (dietInvariant tree)
          //assert (fst <| intervalsDisjoint tree Set.empty)
  
          match tree with
          | Empty ->
  
negative.code:     /// Returns the number of intervals in the set.
      let intervalCount (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
  