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Two concurrent processes $P1$ and $P2$ want to use resources $R1$ and $R2$ in a mutually exclusive manner. Initially, $R1$ and $R2$ are free. The programs executed by the two processes are given below.

\begin{array}{|ll|ll|}\hline & \textbf{Program for P1:} && \textbf{Program for P2:} \\\hline \text{S1:} & \text{While ($R1$ is busy) do no-op;} & \text{Q1:} & \text{While ($R1$ is busy) do no-op;} \\ \text{S2:} & \text{Set $R1$ $\leftarrow$ busy;} & \text{Q2:} & \text{Set $R1$ $\leftarrow$ busy;} \\ \text{S3:} & \text{While ($R2$ is busy) do no-op;} & \text{Q3:} & \text{While ($R2$ is busy) do no-op;} \\ \text{S4:} & \text{Set $R2$ $\leftarrow$ busy;} & \text{Q4:} & \text{Set $R2$ $\leftarrow$ busy;} \\ \text{S5:} & \text{Use $R1$ and $R2$;} & \text{Q5:} & \text{Use $R1$ and $R2$;} \\ \text{S6:} & \text{Set $R1$ $\leftarrow$ free;} & \text{Q6:} & \text{Set $R2$ $\leftarrow$ free;} \\ \text{S7:} & \text{Set $R2$ $\leftarrow$ free;} & \text{Q7:} & \text{Set $R1$ $\leftarrow$ free;} \\\hline \end{array}