anchor.diff:      open OptimizedClosures
   
       /// An empty AVL tree.
  -    let empty : AvlTree<'T> = AvlTree.Empty
  +    let empty : AvlTree<'T> = Empty
   
       /// Returns the height of an AVL tree's root node.
       let inline height (tree : AvlTree<'T>) =
  
positive.code:         let rec diff' input head stream =
              match head with
              | None ->
                  input, None, AvlTree.Empty
              | Some (x, y) ->
                  match input with
                  | AvlTree.Empty ->
                      AvlTree.Empty, head, stream
                  | AvlTree.Node ((a, b), left, right, _) ->
                      let left, head, stream =
                          if x < a then
                              diff' left head stream
  
negative.code:     /// No exception is thrown if any of the values are already contained in the set.
      let rec addRange (p, q) (tree : CharDiet) : CharDiet =
          match tree with
          | Empty ->
              AvlTree.singleton (p, q)
          | Node ((x, y), left, right, _) ->
              if q < pred x then
                  AvlDiet.join (x, y) (addRange (p, q) left) right
              elif p > succ y then
  