anchor.diff:          assert (CharDiet.Height input >= CharDiet.Height stream)
           assert (dietInvariant input)
           assert (dietInvariant stream)
  -//        assert (fst <| intervalsDisjoint input Set.empty)
  -//        assert (fst <| intervalsDisjoint stream Set.empty)
  +        assert (fst <| intervalsDisjoint input Set.empty)
  +        assert (fst <| intervalsDisjoint stream Set.empty)
   
           match head, input with
           | None, _->
  
positive.code:         | Empty ->
              p, Empty
          | Node (left, right, (x, y), _) ->
              if p > succ y then
                  let p', right' = find_del_left p right
                  assert (dietInvariant right')
                  assert (fst <| intervalsDisjoint right' Set.empty)
  
negative.code:                                 assert (dietInvariant x)
                                  assert (fst <| intervalsDisjoint x Set.empty))
  
              elif value < safePred x then
                  CharDiet.Join (comparer, add value left, right, (x, y))
                  |> tap (fun x ->
                      assert (dietInvariant x)
  