anchor.diff:          elif AvlTree.isEmpty stream then
               AvlTree.Empty
           else
  -            let head, stream = AvlTree.extractMin charComparer stream
  +            let head, stream = AvlTree.extractMin stream
               let result, _, _ = inter' input (Some head) stream
               result
   
  
positive.code:             // second traversal to remove the element once it's found.
              let n = create x mid r
              create a left n
              |> extractMin comparer
  
      /// Extracts the minimum (least) value from an AVL tree,
      /// returning the value along with the updated tree.
      /// No exception is thrown if the tree is empty.
      let tryExtractMin (comparer : IComparer<_>) (tree : AvlTree<'T>) =
          // Is the tree empty?
          if isEmpty tree then
              None, tree
          else
              let minElement, tree = extractMin comparer tree
              Some minElement, tree
  
      /// Extracts the maximum (greatest) value from an AVL tree,
      /// returning the value along with the updated tree.
      let rec extractMax (comparer : IComparer<_>) (tree : AvlTree<'T>) =
          match tree with
          | Empty ->
              invalidArg "tree" "The tree is empty."
  
negative.code:             #endif
  
              let head, stream' =
                  AvlTree.tryExtractMin stream
  
              let result, head', stream'' =
                  union' input None head stream'
  