anchor.diff:          | Empty ->
               invalidArg "set" "The set is empty."
           | Lf (_, listSet) ->
  -            ListSet.Last listSet
  +            List.last listSet
           | Br (_, _, _, t1) ->
               PatriciaHashSet.Last t1
   
  
positive.code:             false
          | Lf (j, listSet) ->
              j = valueHash
              && ListSet.Contains (value, listSet)
          | Br (_, m, t0, t1) ->
              PatriciaHashSet.Contains (
                  valueHash, value, (if zeroBit (valueHash, m) then t0 else t1))
  
negative.code:         match set with
          | Empty -> 0
          | Lf (_, listSet) ->
              List.length listSet
          | Br (_,_,_,_) ->
              /// The stack of trie nodes pending traversal.
              let stack = Stack (defaultTraversalStackSize)
  