  The problem of computing modulo prime-power sums is investigated in
distributed source coding as well as computation over Multiple-Access Channel
(MAC). We build upon group codes and present a new class of codes called Quasi
Group Codes (QGC). A QGC is a subset of a group code. These codes are not
closed under the group addition. We investigate some properties of QGC's, and
provide a packing and a covering bound. Next, we use these bounds to derived
achievable rates for distributed source coding as well as computation over MAC.
We show that strict improvements over the previously known schemes can be
obtained using QGC's.
