anchor.diff:  %% @doc Calculate 8 neighboring geohashes
   -spec neighbors(binary()) -> [binary()].
   neighbors(C) ->
  -    N = neighbor(C, u),
  -    W = neighbor(C, l),
  -    S = neighbor(C, d),
  -    E = neighbor(C, r),
  -    NW = neighbor(N, l),
  -    NE = neighbor(N, r),
  -    SW = neighbor(S, l),
  -    SE = neighbor(S, r),
  +    {ok, N} = neighbor(C, n),
  +    {ok, W} = neighbor(C, w),
  +    {ok, S} = neighbor(C, s),
  +    {ok, E} = neighbor(C, e),
  +    {ok, NW} = neighbor(N, w),
  +    {ok, NE} = neighbor(N, e),
  +    {ok, SW} = neighbor(S, w),
  +    {ok, SE} = neighbor(S, e),
       [N, W, S, E, NW, NE, SW, SE].
   
   %% @doc Expand a geohash to give a list of itself and 8 neighboring geohashes
  
positive.code: -spec nearby(float(), float(), float()) -> [binary()].
  nearby(Lat, Lon, Rad) ->
      Precision = nearby_precision(Lat, Lon, Rad),
      GeoHash = encode(Lat, Lon, Precision),
      expand(GeoHash).
  
  %% @private
  
negative.code:     DeltaLat = MaxLat - MinLat,
      DeltaLon = MaxLon - MinLon,
      Bits = geohash_bits(DeltaLat, DeltaLon, 63),
      trunc(Bits/5).
  
  %% @doc Determine the bounding box of coordinates for a point and radius
  %% distance on the earth.
  