We study the two-user interference channel where the source nodes may transmit and receive in half-duplex while the destinations only receive as usual. Depending on the sources, the channel can be in one of three modes: A) both sources transmit, B) source 1 transmits while source 2 receives, and C) source 2 transmits and source 1 receives. This allows a limited form of cooperation between the sources. In this paper, we focus on the corresponding symmetric linear deterministic channel and derive its sum capacity. We consider a scheme which, by operating in modes B and C, transforms mode A into a virtual two-user interference channel with rate-limited bit pipes between the two source nodes and from each source node to the destination node it causes interference to. For the virtual channel so created, we propose a generalization of the superposition coding scheme of Han-Kobayashi to take advantage of the bit pipes. Finally, we derive matching upperbounds to show that the performance of the composite scheme is indeed optimal for the original channel.