[Zope] Sorting on 2 or more properties

Hi all, I am passing a list of objects to a zpt and would like to sort them on 2 or more of the properties. For example I have a class object with the following properties: id professor_name student_name course_number I would like to sort first on the professor_name, then course_number, and then finally student_name. I have googled and can only find examples for sorting on one property at a time. tia, Mike