If you want this functionality, you should use a higher-level apt frontend such as aptitude or deborphan. apt-get is a small, low-level program that's shipped with apt, and it doesn't do this sort of complicated operation (which, among other things, need to store extra state information on disk to work).
Daniel -- /-------------------- Daniel Burrows <[EMAIL PROTECTED]> -------------------\ | Wisdom is one of the few things | | that looks bigger the farther away it is. | | -- Terry Pratchett | \------- Listener-supported public radio -- NPR -- http://www.npr.org --------/

