anchor.diff:                  else
                       Empty
   
  -        | Br (_, m, s0, s1), (Lf k as t) ->
  +        | Br (_, m, s0, s1), Lf k ->
               let s' = if zeroBit (k, m) then s0 else s1
               if PatriciaSet.Contains (k, s') then t
               else Empty
  
positive.code:         match set with
          | Empty ->
              false
          | (Lf j) ->
              key = j
          | Br (_, m, t0, t1) ->
              PatriciaSet.Contains
  
negative.code:                         Br (p, m, s0, right)
              else s
              
          | Br (_,_,_,_), Empty ->
              s
          | Lf k, t ->
              if PatriciaSet.Contains (k, t) then Empty
              else s
          | Empty, _ ->
  