Filter one field based on another field

I would like a filter that shows all tickets WHERE status = "Completed" AND Last External Activity is <= Close Date.

This will show me all tickets that we closed, but have not been updated by API/email/web since we completed them.

...and then I can run the "remove all tickets from inbox" on that set of tickets - because I don't need to review them.

Does that make sense?

Interesting idea, unfortunately while you can filter by each of the fields that you mentioned and have the AND condition between them you currently cannot compare between them. We'll take a note on this. Thanks.