anchor.diff:  -spec empty() -> environment().
   
   empty() ->
  -    [{map, dict:new()}].
  +    [{map, #{}}].
   
   
   %% =====================================================================
  
positive.code: size(Env) ->
      env_size(Env).
  
  env_size([{map, Dict}]) ->
      dict:size(Dict);
  env_size([{map, Dict} | Env]) ->
      dict:size(Dict) + env_size(Env);
  env_size([{rec, Dict, _Dict0} | Env]) ->
      dict:size(Dict) + env_size(Env).
  
  
  %% =====================================================================
  
negative.code: 
  -spec lookup(term(), environment()) -> 'error' | {'ok', term()}.
  
  lookup(Key, [{map, Map} | Env]) ->
      case maps:find(Key, Map) of
  	{ok, _}=Value ->
  	    Value;
  	error when Env =:= [] ->
  