anchor.diff:  
               let result =
                   let result, head', stream'' =
  -                    let head, stream' = AvlTree.tryExtractMin stream
  +                    let head, stream' = AvlTree.TryExtractMin stream
                       union' input None head stream'
   
                   match head' with
                   | None ->
                       result
                   | Some i ->
  -                    AvlDiet.join i result stream''
  +                    AvlTree.Join comparer i result stream''
   
               #if DEBUG
               let resultCount = count result
  
positive.code:                     if q <= y then y, right
                      else find_del_right q right
  
                  AvlDiet.join (x', y') left' right'
  
      /// Returns a new set with the given element removed.
      /// No exception is thrown if the set doesn't contain the specified element.
  
negative.code:         match tree with
          | Empty ->
              p, Empty
          | Node (left, right, (x, y), _) ->
              if p < pred x then
                  let p', left' = find_del_right p left
                  p', AvlTree.Join comparer (x, y) left' right
              elif p > y then
                  find_del_right p right
              else
  