this setup. The authors in [@NagMohMurKis_11], proposed the achievable rate regions for the different non-causal message-sharing mechanism in the three-user C-IFC and also derived an outer bound in the Gaussian case.

In this paper, we consider a *three-user* C-IFC with *two* primary users and *one* cognitive user, where the cognitive transmitter non-causally knows the messages of both primary transmitters. Up to our best knowledge, in all of the previous works on *three-user* C-IFC in the general discrete memoryless setup, only achievable rate regions have been obtained and the capacity result in all setups of *three-user* C-IFC is an open problem. In this paper, we consider the strong interference regime and derive *capacity regions* in this case. First, we obtain two inner bounds on the capacity region (achievable rate regions) based on using superposition coding and allowing all receivers to decode all messages. In the achievablity scheme of the first region, we utilize simultaneous joint decoding in the decoding part at all receivers. However, in the second scheme, each primary receiver first decodes the other primary user’s message, while treating the remaining signals as noise, i.e., the combination of its intended transmitter’s signal, the cognitive transmitter’s signal and additive noise. This 