Abstract- We indicate the dependence between the inputs of the relay channel with one auxiliary random variable as Cover, El-Gamal and Salehi have done so for the multiple access channel with arbitrarily correlated sources. Then, by considering broadcast and multiple access sub-channels in the relay channel, we describe the essential role of the relay with special Markovity conditions on the auxiliary random variable and channel input-outputs, and unify most of known capacity theorems into one capacity theorem. Our capacity theorem potentially may be applicable to a more general class of relay channels including at least the relay channels with known capacity.

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