Question: My parking permit at the university gives me rights to use a very convenient lot reserved exclusively for faculty. Even if I arrive at a peak hour like 10 a.m. I can almost surely find a space in it. Your student permit allows you to park in an inconvenient lot that is often full by 9 a.m., sometimes forcing you to use an overflow lot and take a bus to campus. We would both be better off after a trade in which you paid me $100 for my permit and in return I used yours. Why might the school's administration make trades like these illegal even though they leave us both better off?