Oracle: list of the system events

SET serveroutput ON
 DECLARE
  event_level NUMBER;
 BEGIN
  dbms_output.enable(20000) ;
  FOR i IN 10000..33999 LOOP
     sys.dbms_system.read_ev(i,event_level);
     IF (event_level > 0) THEN
        dbms_output.put_line('Event '||to_char(i)||' set at level '||
                             TO_CHAR(event_level));
     END IF;
  END LOOP;
END;