[Zope] checking for elements in a list

Hello, I'm am trying to check for the membership of items in a list and think I'm missing something. How is this done in dtml? List allids: [15,16,17,18] Check for multiple items in the list: <dtml-in allids prefix="loop"> <dtml-if expr="loop_item == 17"> something <dtml-elif expr="loop_item == 17 and loop_item != 18"> doesn't work </dtml-if> </dtml-in> The goal is to check for combinations: 17 and not 18 18 only 17 only 17 and 15 18 and 16 ...combinations. I don't think that I really want to loop through the list, just want to check membership in the list. Thanks in advance, Chris