anchor.diff:  
   find(_,_) -> erlang:nif_error(undef).
   
  -
  +%% Shadowed by erl_bif_types: maps:from_list/1
   -spec from_list(List) -> Map when
       List :: [{Key,Value}],
       Key :: term(),
  
positive.code:          new/0, put/3, remove/2, take/2,
           to_list/1, update/3, values/1]).
  
  -spec get(Key,Map) -> Value when
      Key :: term(),
      Map :: map(),
  
negative.code: from_list(_) -> erlang:nif_error(undef).
  
  
  %% Shadowed by erl_bif_types: maps:is_key/2
  -spec is_key(Key,Map) -> boolean() when
      Key :: term(),
      Map :: map().
  