9. Consider the following precedence relations between processes: .PO do S1 before P1, P3 and P6 P3 do S3 before P5 P6 do S6 before P5 PO after P2 and P4 where Pi before Pj means that the execution of Pi must be completed before the execution of Pj starts, and Pi after Pj is conversely defined. (a) (2 points) Draw a process precedence graph for the above processes. (b) (6 points) Using semaphores, write each process that enforce the above precedence rela- tions. Make sure to properly initialize each semaphore.