We consider a communication system in which two sources communicate with a destination with the help of a common relay. We assume that the relay operates in half-duplex mode; and concentrate on the symmetric-rate case. We study and analyse the performance of a simple strategy in which the relay simply amplifies its output and retransmits it. However, unlike standard amplify-and-forward, the destination recovers the sent messages by computing and inverting two appropriate linear combinations of the sources' messages, obtained using what it gets from the sources and the relay. We discuss the design criteria and establish the sum-rate allowed by this strategy. Also, we consider, and solve, the problem of maximizing the sum-rate by properly optimizing the power values and the integer-valued coefficients of the recovered linear combinations. It should be emphasized that although the coding strategy described in this paper performs only as good as standard amplify-and-forward, it has the advantage of utilizing simpler linear codes; and, so, is more relevant in practical collaborative systems.