anchor.diff:          _ ->
               [{line,?LINE},{expected, Keys},{received, R}]
       end;
  -postcondition(_From, _To, S,
  +postcondition(_From, _To, #qcst{backend=Backend}=S,
                 {call, _M, fold_keys, [_FoldFun, _Acc, [{bucket, B}], _BeState]}, FoldRes) ->
       ExpectedEntries = orddict:to_list(S#qcst.d),
       Keys = [{Bucket, Key} || {{Bucket, Key}, _} <- ExpectedEntries, Bucket == B],
  
positive.code:     case lists:sort(Keys) =:= lists:sort(R) of
          true -> true;
          _ ->
              [{line,?LINE},{expected, Keys},{received, R}]
      end;
  postcondition(_From, _To, S,
                {call, _M, fold_objects, [_FoldFun, _Acc, _Opts, _BeState]}, FoldRes) ->
  
negative.code:     case lists:sort(Keys) =:= lists:sort(R) of
          true -> true;
          _ ->
              try
                  Backend:backend_eqc_postcondition_fold_keys(Keys, R)
              catch
                  error:undef ->
                      [{line,?LINE},{expected, Keys},{received, R}]
              end
      end;
  postcondition(_From, _To, #qcst{backend=Backend}=S,
                {call, _M, fold_keys, [_FoldFun, _Acc, _Opts, _BeState]}, FoldRes) ->
      ExpectedEntries = orddict:to_list(S#qcst.d),
      Keys = [{Bucket, Key} || {{Bucket, Key}, _} <- ExpectedEntries],
  