anchor.diff:          false ->
               S1
       end;
  +next_state_data({running,Backend,Volatile},{stopped,Backend,Volatile},S,_R,
  +                {call,_M,drop,_}) ->
  +    S#qcst{s=undefined, olds=sets:add_element(S#qcst.s, S#qcst.olds),
  +           d=orddict:new()};
   next_state_data(_From,_To,S,BeState,{call,_M,init_backend,_}) ->
       S#qcst{s = BeState};
   next_state_data(_From,_To,S,_R,{call,_M,put,[_S, Key, Val]}) ->
  
positive.code:      {history, {call,Backend,delete,[S#qcst.s,bkey()]}},
       {history, {call,Backend,list,[S#qcst.s]}},
       {history, {call,?MODULE,fold,[Backend,S#qcst.s]}},
       {{stopped, Backend, Volatile}, {call,Backend,stop,[S#qcst.s]}}
      ].
  
  
negative.code: initial_state_data(Config) ->
      #qcst{c = Config, d = orddict:new()}.
  
  next_state_data({running,Backend,Volatile},{stopped,Backend,Volatile},S,_R,
                  {call,_M,stop,_}) ->
      S1 = S#qcst{s = undefined, olds = sets:add_element(S#qcst.s, S#qcst.olds)},
      case Volatile of
          true ->
  