1. Original Version
2. Change the order of calls to create_thread
3. remove both calls to join
4. remove both calls to yield
5. remove both calls to yield and join
6. remove both calls to yield, and one of the joins. Is the result dependent on which join is removed?
7. remove pong¡¯s yield and ping¡¯s join
8. remove pong¡¯s yield and pong¡¯s join
9. change uthread_init call to take 2 CPUs
10. Change the yield in ping to a block
11. What is the output for the program below