anchor.diff:  
       //
       // TODO : This could be replaced by 'mkt_bal_l' and 'mkt_bal_r'.
  -    static member Balance (l, r, n) : AvlTree<'T> =
  +    static member private Balance (l, r, n) : AvlTree<'T> =
           // Preconditions
           assert (AvlTree.AvlInvariant l)
           assert (AvlTree.AvlInvariant r)
  
positive.code: 
              elif x > b && x > succ b then
                  let right', head, stream = union' right limit head stream
                  (tapInvariant <| CharDiet.Join (comparer, left, right', (a, b))), head, stream
  
              elif b >= y then
                  CharDiet.TryDeleteMin stream
  
negative.code:             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))
  
                  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))
  
                  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
  