TicketSQL -- how to search for a member of a group?

My question touches on some issues that are similar to “Search for open
tickets last updated by requestor” (https://lists.gt.net/rt/users/51042)

I have a search set up for closed bugs updated within the last day, where
the update is not by the current user:

Owner = 'CurrentUser
AND LastUpdatedBy != 'CurrentUser
AND LastUpdated > '1 day ago’
AND Status != 'new’
AND Status != 'open’
AND Status != 'onhold’
AND Status != ‘needsinfo’

We have this as part of a dashboard that’s sent daily to staff – we want
to alert the staff of any closed tickets that some requester has touched.

That’s all well and good, but there are times when tickets get mass-updated
by members of our staff, and because that staff member is not
CurrentUser, we get spammed by those.

We do have a group called ‘Staff’, so I should be able to do something like
this:

Owner = 'CurrentUser
AND LastUpdatedBy != 'CurrentUser
AND LastUpdatedBy IS NOT A MEMBER OF STAFF
AND LastUpdated > '1 day ago’
AND Status != 'new’
AND Status != 'open’
AND Status != 'onhold’
AND Status != ‘needsinfo’

… I just need to know how to express " IS NOT A MEMBER OF STAFF" as
TicketSQL.

… this was touched upon as a possible solution for “Search for open
tickets last updated by requestor”, but the syntax wasn’t given.

Thanks,

–Barton