anchor.diff:          match set with
           | Empty ->
               Empty
  -        | (Lf j) as t ->
  +        | Lf j ->
               if j = key then Empty
  -            else t
  -        
  -        | Br (p, m, t0, t1) as t ->
  +            else set
  +        
  +        | Br (p, m, t0, t1) ->
               if matchPrefix (key, p, m) then
                   if zeroBit (key, m) then
                       match PatriciaSet.Remove (key, t0) with
  
positive.code:         | Br (_,_,_,_), (Empty | Lf _) -> 1
          | Lf x, Lf y ->
              if x = y then 0
              else 1  // The maps are disjoint.
  
          | Lf x, Br (p, m, l, r) ->
              if not <| matchPrefix (x, p, m) then 1
              elif zeroBit (x, m) then
                  match PatriciaSet.SubsetCompare (t1, l) with
                  | 1 -> 1
                  | _ -> -1
              else
                  match PatriciaSet.SubsetCompare (t1, r) with
                  | 1 -> 1
                  | _ -> -1
  
          | Lf _, Empty ->
              // The maps are disjoint.
  
negative.code:                     | Empty -> t0
                      | t1 ->
                          Br (p, m, t0, t1)
              else set
  
      //
      static member inline private Join (p0, t0 : PatriciaSet, p1, t1) =
  