anchor.diff:  
   %%% End of BIFs
   
  --spec foldl(Fun,Init,Map) -> Acc when
  +-spec fold(Fun,Init,Map) -> Acc when
       Fun :: fun((K, V, AccIn) -> AccOut),
       Init :: term(),
       Acc :: term(),
  
positive.code:     K :: term(),
      V :: term().
  
  foldl(Fun, Init, Map) when is_function(Fun,3), is_map(Map) ->
      lists:foldl(fun({K,V},A) -> Fun(K,V,A) end,Init,maps:to_list(Map)).
  
  -spec foldr(Fun,Init,Map) -> Acc when
      Fun :: fun((K,V,AccIn) -> AccOut),
      Init :: term(),
      Acc :: term(),
      AccIn :: term(),
      AccOut :: term(),
      Map :: map(),
      K :: term(),
      V :: term().
  
  foldr(Fun, Init, Map) when is_function(Fun,3), is_map(Map) ->
      lists:foldr(fun({K,V},A) -> Fun(K,V,A) end,Init,maps:to_list(Map)).
  
  
  -spec map(Fun,Map1) -> Map2 when
      Fun :: fun((K, V1) -> V2),
  
negative.code: -module(maps).
  
  -export([
  	fold/3,
  	map/2,
  	size/1,
  	without/2
  