anchor.diff:  next_state(State, _Res, _Call) ->
   	State.
   
  -extract_location_header({ok, _State, Headers, _Body}) ->
  +extract_location_header({ok, _State, Headers, _Body} = R) ->
   	proplists:get_value("Location", Headers);
   
   extract_location_header(Res) ->
  
positive.code: 	] end}}.
  
  prop_map_statem() ->
  	?FORALL(Cmds, proper_statem:commands(?MODULE), begin
  		{_Hist, _State, Res} = run_commands(?MODULE, Cmds),
  		Res == ok
  	end).
  
  initial_state() ->
  	#state{}.
  
  command(State) ->
  	frequency([
  		{1, {call, ?MODULE, create_map, [g_mapjson(), State]}},
  		{1, {call, ?MODULE, destroy_map, [State]}},
  		{5, {call, ?MODULE, update_map, [g_mapjson(), State]}}
  	]).
  
  %% =======================================================
  
negative.code: %% postcondition
  %% =======================================================
  
  postcondition(State, {call, _, create_map, [Json, InState]}, {ok, "201", Heads, Body} = Goop) ->
  	?assertNotEqual(undefined, proplists:get_value("Location", Heads)),
  	?assert(assert_body(Json, Body)),
  	true;
  