Question 4. a) Consider a system of two processes P and Q that are regarded to be connected by unidirectional channels c and c' as shown in the following figure. During a computation, P sends messages m1, m2, and m3 to Q in that order, and Q sends to P messages M1, M2, and M3 in that order. S1, S2, S3, and S4 are four global states encountered in that order during the computation and are depicted only partially in the Table below. For simplicity, the state of a process in a given global state is expressed as an ordered sequence of messages it has sent and received in that global state. For example, P's state in S1 being means that P has sent m1, sent m2, and received M1 in that order; state of channel c in S2 being means that channel c has no message in S2. Without modifying the global state components shown in the table, determine the global states, given that send(m2) send(M2) and send(M3) send(m3) hold during the computation. c' Q Global State S1 ? ? S2 ? ? ? S3 ? ? S4 ?