Oracle: list of the system events

This piece of code show the list of events, set in the Oracle database

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;