2772	 On Maintenance of the Opportunity List for Class-Teacher Timetable Problems	 One of the principal components of procedures for the solution of class-teacher timetable problems is that for maintenance of the opportunity list. Opportunity list maintenance methods are based on necessary conditions for the existence of a solution. A general framework for necessary conditions together with four specific sets of necessary conditions is given. combinatorial necessary conditions opportunity list schedule school timetable timetable
