anchor.diff:              AvlTree.Insert (comparer, l, root)
           | Node (ll, lr, ln, lh), Node (rl, rr, rn, rh) ->
               if lh > rh + balanceTolerance then
  -                let r' =
  -                    AvlTree.Join (comparer, lr, r, root)
  -                    |> tap (fun x -> assert (AvlTree.AvlInvariant x))
  -
  +                let r' = AvlTree.Join (comparer, lr, r, root)
                   AvlTree.Balance (ll, r', ln)
  -                |> tap (fun x -> assert (AvlTree.AvlInvariant x))
               elif rh > lh + balanceTolerance then
  -                let l' =
  -                    AvlTree.Join (comparer, l, rl, root)
  -                    |> tap (fun x -> assert (AvlTree.AvlInvariant x))
  -
  +                let l' = AvlTree.Join (comparer, l, rl, root)
                   AvlTree.Balance (l', rr, rn)
  -                |> tap (fun x -> assert (AvlTree.AvlInvariant x))
               else
                   AvlTree.Create (root, l, r)
  -                |> tap (fun x -> assert (AvlTree.AvlInvariant x))
   
       /// Reroot of balanced trees.
       /// Takes two trees representing disjoint sets and combines them, returning
       /// a new balanced tree representing the union of the two sets.
       static member Reroot (comparer, l, r : AvlTree<'T>) : AvlTree<'T> =
           // Preconditions
  -        assert (AvlTree.AvlInvariant l)
  -        assert (AvlTree.AvlInvariant r)
  +        //assert (AvlTree.AvlInvariant l)
  +        //assert (AvlTree.AvlInvariant r)
   
           match l, r with
           | Empty, Empty ->
  
positive.code:     /// any difference in height between the trees.
      static member Join (comparer, l, r : AvlTree<'T>, root) : AvlTree<'T> =
          // Preconditions
          assert (AvlTree.AvlInvariant l)
          assert (AvlTree.AvlInvariant r)
  
          match l, r with
          | Empty, Empty ->
  
negative.code:     /// Returns the number of intervals in the set.
      let intervalCount (tree : CharDiet) =
          // Preconditions
          //assert (dietInvariant tree)
          //assert (fst <| intervalsDisjoint tree Set.empty)
  
          // OPTIMIZE : Modify this to use a mutable stack instead of an F# list.
          let rec cardinal_aux acc = function
  