```
create or replace trigger trig1
before delete or insert or update on students 
begin
if( To_char(sysdate,'day') = 'monday' then
raise_application_error(-20500,'table is secured');
end if;
end;

```

I create trigger but it is not working for `monday` and it performs DML actions on table. I found one solution - to use dy instead of day - but why?