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Rank-deficient multiple-input multiple-output (MIMO) relay interference channel (IC) is investigated in which K source-destination pairs communicate with the help of N relays. For the K-user rank-deficient MIMO IC with no relays, an achievable sum degrees of freedom (DoF) is upper bounded by Krds, where rds denotes the rank of each point-to-point channel matrix. However, if relays assist the communication, we show that there can be significant improvement on the DoF compared to the case where there is no relay. The proposed cooperative relaying uses relays not only for increasing ranks of desired channel matrices but also nullifying inter-user interference.