anchor.diff:              && AvlTree.AvlInvariant r
   
       /// Returns the height of a AvlTree.
  +    [<Pure>]
       static member inline Height (tree : AvlTree<'T>) =
           match tree with
           | Empty -> 0u
           | Node (_,_,_,h) -> h
   
       /// Determines if a AvlTree is empty.
  +    [<Pure>]
       static member inline IsEmptyTree (tree : AvlTree<'T>) =
           match tree with
           | Empty -> true
  
positive.code: 
                  assert (dietInvariant left')
                  assert (dietInvariant right')
                  AvlTree.Join (comparer, left', right', (x', y'))
  
      /// Returns a new set with the given element removed.
      /// No exception is thrown if the set doesn't contain the specified element.
  
negative.code:         }
  
      /// Returns a list containing the elements stored in
      /// a AvlTree, ordered from least to greatest.
      static member ToList (tree : AvlTree<'T>) =
          ([], tree)
          ||> AvlTree.FoldBack (fun el lst ->
  