Capacity region is the region which can be achieved by multiple users in a communication network. In particular, if there are $ K $ users in a network and $ (R_1, R_2, \ldots, R_K) $ is a point of K-user capacities. Given the capacity region, $ (R_1, R_2, \ldots, R_K) $ can be achieve lower than the capacity region of $ \{R(R_1, R_2, \ldots, R_K)|C(R) > 0\} $.

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