anchor.diff:      K :: term(),
       V :: term().
   
  -foldl(Fun, Init, Map) ->
  +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
  
positive.code:     V1 :: term(),
      V2 :: term().
  
  map(Fun, Map) ->
      maps:from_list(lists:map(fun
  		({K,V}) ->
  		    {K,Fun(K,V)}
  
negative.code: -spec size(Map) -> non_neg_integer() when
      Map :: map().
  
  size(Map) when is_map(Map) ->
      erlang:map_size(Map).
  
  
  -spec without(Ks,Map1) -> Map2 when
      Ks :: [K],
  