anchor.diff:  find_node(X, [{X1, Y}, {X, Y} | Nodes], Acc) ->
       {X, X1, Nodes ++ Acc};
   find_node(X, [{X, _Y} | _], _Acc) ->
  -  {error, ?POW_DEAD_END};
  +    {error, ?POW_DEAD_END};
   find_node(X, [N1, N2 | Nodes], Acc) ->
  -  find_node(X, Nodes, [N1, N2 | Acc]).
  +    find_node(X, Nodes, [N1, N2 | Acc]).
   
   %%------------------------------------------------------------------------------
   %% @doc
  
positive.code: %%   Stop the OS process
  %% @end
  %%------------------------------------------------------------------------------
  -spec stop_execution(integer()) -> ok.
  stop_execution(OsPid) ->
      exec_kill(OsPid),
      ?debug("Mining OS process ~p stopped", [OsPid]),
  
negative.code: 
  -define(debug(F, A), epoch_pow_cuckoo:debug(F, A)).
  -define(info(F, A),  epoch_pow_cuckoo:info(F, A)).
  -define(warning(F, A), epoch_pow_cuckoo:warning(F, A)).
  -define(error(F, A), epoch_pow_cuckoo:error(F, A)).
  
  -type os_pid() :: integer() | undefined.
  -type pow_cuckoo_solution() :: [integer()].
  
  -record(state, {os_pid :: os_pid(),
                  port :: port() | undefined,
                  buffer = [] :: string(),
                  target :: aec_pow:sci_int() | undefined,
                  parser :: output_parser_fun()}).
  
  -type output_parser_fun() :: fun((list(string()), #state{}) ->
                                          {'ok', term(), term()} | {'error', term()}).
  
  