map<timetable_sort_criterion, string> GetTimetableSortCriteria(bool has_alternate_timeslots);

Get the possible criteria by which a timetable can be sorted. Each criterion is represented by an identifier of type timetable_sort_criterion, and a user-facing string that describes the criterion. Clients should show the user the list of user-facing strings, have the user select some criteria, and pass in the identifiers of the selected criteria to SortTimetables.

Since one of the criteria is "balance between 'week 1' and 'week 2'" which only applies to timetables with alternate-week labs, one must pass in whether or not the timetables to be sorted have alternate-week labs, and this criterion will be part of the returned list, or not, accordingly.