How to tell which event was fired in Trigger function

Hi,

I am writing a trigger function that is used after DELETE, INSERT, and UPDATE, like so:

    CREATE TRIGGER tr_name AFTER DELETE OR INSERT OR UPDATE ...

How can I tell inside the trigger function if the event was DELETE or INSERT/UPDATE? 

The table has a `NOT NULL id` column, so I am thinking that maybe a DELETE will have a NULL value in NEW.id?  Will that work?  Is there a better way?

Thanks,