anchor.diff:          match tree with
           | Empty ->
               Empty
  -        | Node (left, right, (x, y), h) ->
  +        | Node (left, right, (x, y), _) ->
               let czx = compare value x
               if czx < 0 then
                   // value < x, so recurse down the left subtree.
  
positive.code: 
      /// Returns 'true' if the set is empty.
      [<CompiledName("IsEmpty")>]
      let inline isEmpty charSet =
          CharSet.IsEmpty charSet
  
      /// Returns the number of elements in the set.
  
negative.code:         match tree with
          | Empty ->
              singleton value
          | Node (left, right, (x, y), _) ->
              if value >= x then
                  if value <= y then
                      // The value is already in [x, y] so the tree
  