anchor.diff:      //
       static member private SubmapCmp (predicate : 'T -> 'T -> bool) (t1 : PatriciaMap<'T>) (t2 : PatriciaMap<'T>) : int =
           match t1, t2 with
  -        | (Br (p1, m1, l1, r1) as t1), (Br (p2, m2, l2, r2) as t2) ->
  +        | Br (p1, m1, l1, r1), Br (p2, m2, l2, r2) ->
               if shorter (m1, m2) then 1
               elif shorter (m2, m1) then
                   if not <| matchPrefix (p1, p2, m2) then 1
  
positive.code:                     match PatriciaMap.Delete (k, s0) with
                      | Empty -> s1
                      | left ->
                          Br (p, m, left, s1)
                  else
                      match PatriciaMap.Delete (k, s1) with
                      | Empty -> s0
                      | right ->
                          Br (p, m, s0, right)
              else s
              
          | Br (_,_,_,_) as s, Empty ->
              s
          | (Lf (k, x) as s), t ->
              if PatriciaMap.ContainsKey (k, t) then Empty
              else s
          | Empty, _ ->
  
negative.code:         match map with
          | Empty ->
              Empty
          | Lf (j, _) ->
              if key = j then Empty
              else map
          | Br (p, m, t0, t1) ->
              if matchPrefix (key, p, m) then
                  if zeroBit (key, m) then
                      match PatriciaMap.Delete (key, t0) with
  