  We investigate whether the use of a noiseless, classical feedback channel
will increase the capacity of a quantum discrete memoryless channel to transmit
classical information. This problem has been previously analyzed by Bowen and
Nagarajan for the case of protocols restricted to product input states. They
showed that feedback did not increase the information capacity. In this paper
we introduce a quantum analogue of classical causality and prove a capacity
theorem (in regularized form) for the transmission of classical information.
