Is-iff
From FreeSpace Wiki
Is IFF (Boolean operator) True if ship{s} are all of the specified team. Returns a boolean value; Takes 2 or more arguments: /t1: Team ("friendly", "hostile" or "unknown"). Rest: Name of ship to check.
Comments
The retail version of this SEXP does not work for many people—it crashes in both FS1 and FS2. This is fixed in FSO, which also allows it to be used on wings.