Apologies for not sending out an email about this week's meeting, which of course didn't take place because many of us are here in Leysin. But let me already announce next week's talk, which will be on _Monday_ at 1600 in E41.1. The talk will be given by Zhengwei Liu, who is visiting from Harvard. The title and abstract are below; it may look quite a bit abstract, but from chatting with him here, I believe there are concrete applications of their formalism to things like, for example, circuit optimization.