An information inequality and evaluation of Marton's inner bound for binary input broadcast channels

We establish an information inequality that is intimately connected to the evaluation of the sum rate given by Marton's inner bound for two-receiver broadcast channels with a binary input alphabet. This generalizes a recent result where the inequality was established for a particular channel, the binary skew-symmetric broadcast channel. The inequality implies that randomized time-division strategy indeed achieves the sum rate of Marton's inner bound for all binary input broadcast channels.