Overworked and over-caffeinated, the Teaching Assistant’s (TA’s) decide to oust the lecturer and teach their own recitations. They will run a recitation session at 4 different times in the same room. There are exactly 20 chairs to which a student can be assigned in each recitation. Each student has provided the TA’s with a list of the recitation sessions her schedule allows and no student’s schedule conflicts with all 4 sessions. The TA’s must assign each student to a chair during recitation at a time she can attend, if such an assignment is possible.

Describe how to model this situation as a matching problem. Be sure to specify what the vertices/edges should be and briefly describe how a matching would determine seat assignments for each student in a recitation that does not conflict with his schedule. This is a modeling problem —you need not determine whether a match is always possible.