On multiple access channels with feedback

For the binary erasure multiple access channel, van der Meulen showed in his survey paper that the symmetrical rate pair (0.79113, 0.79113) is achievable in the case of feedback. Here we prove that this rate point is on the boundary of the feedback capacity region/Subsequently we apply this result to demonstrate the fact that the feedback capacity region of the product of two multiple access channels can be strictly larger than the (Minkowski) sum of the feedback capacity regions for the separate channels.