  Approximate capacity regions are established for a class of interfering
multiple access channels consisting of two multiple-access channels (MACs),
each with an arbitrary number of transmitters, with one transmitter in each MAC
causing interference to the receiver of the other MAC, a channel we refer to
henceforth as the MAC-IC-MAC. For the discrete memoryless (DM) MAC-IC-MAC, two
inner bounds are obtained that are generalizations of prior inner bounds for
the two-user DM interference channel (IC) due to Chong {\em et al}. For the
semi-deterministic MAC-IC-MAC, it is shown that single-user coding at the
non-interfering transmitters and superposition coding at the interfering
transmitter of each MAC achieves a rate region that is within a quantifiable
gap of the capacity region, thereby extending such a result for the two-user
semi-deterministic IC by Telatar and Tse. For the Gaussian MAC-IC-MAC, an
approximate capacity region that is within a constant gap of the capacity
region is obtained, generalizing such a result for the two-user Gaussian IC by
Etkin {\em et al}. Contrary to the aforementioned approximate capacity results
for the two-user IC whose achievability requires the union of all admissible
input distributions, our gap results on the semi-deterministic and the Gaussian
MAC-IC-MAC are achievable by only a subset and one of all admissible coding
distributions, respectively. The symmetric generalized degrees of freedom
(GDoF) of the symmetric Gaussian MAC-IC-MAC with more than one user per cell,
which is a function of the interference strength (the ratio of INR to SNR at
high SNR, both expressed in dB) and the numbers of users in each cell, is
V-shaped with flat shoulders. ...
