anchor.diff:  
   precondition(S, {call, _, create_zone, _}) ->
   	true;
  +precondition(S, {call, _, create_aura, _}) ->
  +	true;
   precondition(S, {call, _, delete_zone, [_, #state{zones = Z}]}) when length(Z) >= 1 ->
   	true;
   precondition(_,_) ->
  
positive.code: command(S) ->
  	oneof([
  		{call, ?MODULE, create_zone, [g_zone(), rpgb_prop:g_name(), g_next(zone, S), S]},
  %		{call, ?MODULE, create_aura, [g_aura(), g_name(), g_layer(), g_next(aura, S), oneof(['owner', 'partier1', 'partier2']), S]},
  %
  %		{call, ?MODULE, create_zone_bad_user, [g_zone(), g_name(), g_layer(), g_next(zone, S), oneof(['partier1', partier2, baduser]), S]},
  %		{call, ?MODULE, create_aura_bad_user, [g_aura(), g_name(), g_layer(), g_next(aura, S), S]},
  
negative.code: 	Json3 = purge_undef(Json2),
  	ibrowse:send_req(?zone_url, [owner_cookie(), ?accepts, ?contenttype], put, jsx:to_json(Json3)).
  
  create_aura(Aura, Name, Next, Who, State) ->
  	#state{auras = Auras} = State,
  	NextZoneId = get_next(Next, Auras),
  	Json = [{<<"next_zone_id">>, NextZoneId} | Aura],
  	Json2 = [{<<"name">>, Name} | proplists:delete(<<"name">>, Json)],
  	Json3 = purge_undef(Json2),
  	Cookie = cookie(Who),
  	ibrowse:send_req(?aura_url, [Cookie, ?accepts, ?contenttype], put, jsx:to_json(Json3)).
  
  delete_zone(Nth, State) ->
  	#state{zones = Zones} = State,
  	Zone = lists:nth(Nth, Zones),
  