Consider the following snapshot of a system running n processes. Process i is holding x_i instances of a resource R, 1$\le$ i$\le$ n. currently, all instances of R are occupied. Further, for all i, process i has placed a request for an additional y_i instances while holding the x_i instances it already has. There are exactly two processes p and q such that 0. y_p = y_q = 0. Which one of the following can serve as a necessary condition to guarantee that the system is not approaching a deadlock?