anchor.diff:  -type maybe_lid() :: lid:lid() | 'not_found'.
   
   %% Tuples providing information about a process' action.
  --type proc_action() :: {'halt', lid:lid()} |
  -                       {'block', lid:lid()} |
  +-type proc_action() :: {'block', lid:lid()} |
   		       {'demonitor', lid:lid(), maybe_lid()} |
                          {'exit', lid:lid(), term()} |
  +                       {'halt', lid:lid()} |
                          {'link', lid:lid(), maybe_lid()} |
   		       {'monitor', lid:lid(), maybe_lid()} |
   		       {'process_flag', lid:lid(), 'trap_exit', boolean()} |
  
positive.code:     io_lib:format("Process ~s unregisters process `~p`",
                    [lid:to_string(Proc), RegName]);
  to_string({whereis, Proc, RegName, not_found}) ->
      io_lib:format("Process ~s attempts to obtain the pid of unregistered "
  		  "process `~p` (undefined)",
                    [lid:to_string(Proc), RegName]);
  to_string({whereis, Proc, RegName, RegLid}) ->
      io_lib:format("Process ~s obtains the pid of process `~p` (~s)",
                    [lid:to_string(Proc), RegName, lid:to_string(RegLid)]).
  
negative.code: 		  [lid:to_string(Proc1), lid:to_string(Proc2)]);
  to_string({exit, Proc, Reason}) ->
      io_lib:format("Process ~s exits (~p)", [lid:to_string(Proc), Reason]);
  to_string({halt, Proc}) ->
      io_lib:format("Process ~s halts the system", [lid:to_string(Proc)]);
  to_string({link, Proc, not_found}) ->
      io_lib:format("Process ~s links to nonexisting process",
  		  [lid:to_string(Proc)]);
  