  This paper establishes the fundamental limits of a two-user single-receiver
system where communication from User 1 (but not from User 2) needs to be
undetectable to an external warden. Our fundamental limits show a tradeoff
between the highest rates (or square-root rates) that are simultaneously
achievable for the two users. Moreover, coded time-sharing for both users is
fundamentally required on most channels, which distinguishes this setup from
the more classical setups with either only covert users or only non-covert
users. Interestingly, the presence of a non-covert user can be beneficial for
improving the covert capacity of the other user.
