How to easily switch between (non)digested list?

Hi, Can anyone please give me a pointer or example: I would like my non-technical list-subscribers to be able to easily switch between a normal and a digested list. So that when they subscribe to one, while already subscribed to the other, the original subscription is (silently) removed. I didn't find a reference on how to do this in the manual or faq. Is there a reason that I shouldn't want to do this? Next-best solution would be to implement an extra "switch" command, may be... Is there a way to do this, without a lot of editing of the sources? Gyelt -- http://www.xs4all.nl/~gyelt/ergo/index.html about Dutch occupational therapy