*35. Students who want to enroll in Model Railroad- ing II at the local university are required to obtain permission from the instructor and pay a laboratory fee. The two requirements are ful- filled independently in either order and at different locations on campus. Enrollment is limited to twenty students; this limit is main- tained by both the instructor, who will grant permission to only twenty students, and the financial office, which will allow only twenty students to pay the laboratory fee. Suppose that this registration system has resulted in nineteen students having successfully registered for the course, but with the final space being claimed by two students—one who has only obtained permission from the instructor and another who has only paid the fee. Which requirement for deadlock is removed by each of the follow- ing solutions to the problem?

1. Both students are allowed in the course.

2. The class size is reduced to nineteen, so neither of the two students is allowed to register for the course.

3. The competing students are both denied entry to the class and a third student is given the twentieth space.

4. It is decided that the only requirement for entry into the course is the payment of the fee. Thus the student who has paid the fee gets into the course, and entry is denied to the other student.