Some libraries, including Portland’s downtown branch, have already instituted an exclusion system to penalize bad behavior: one day for shaving in the bathroom, three years for fighting. But the Philadelphia Free Library, in partnership with Project H.O.M.E., a local nonprofit, has a more enterprising program. It pays homeless patrons to monitor the restrooms, and it plans to employ them at a new café. Participation in the program, like the library, is open to all.