Multiple values for check items - silly question

Hi, This more than likely goes back to using the correct OP values, so I'm hoping someone can shed some light on this. I have a groupcheck requirement that requires a value of a attribute to be either one, or the other. NAS-Port-Type := ISDN, NAS-Port-Type := Virtual Now, obviously I can't add it like the above. I will only receive ISDN *or* Virtual, not both. What OP should I use to make it check of one or the other? Thanks, Chris