  In this paper, the Two-Way Channel (TWC) with Cannel State Information (CSI)
is investigated. First, an achievable rate region is derived for the discrete
memoryless channel. Then by extending the result to the Gaussian TWC with
additive interference noise, it is shown that the capacity region of the later
channel is the same as the capacity when there is no interference, i.e. a
two-way version of Costa's writing on dirty paper problem is established.
