"Cyclic Combinational Circuits", by Marc D. Riedel
> we present theoretical justification for the claim that the optimal form of some [combinational] circuits requires cyclic topologies. We exhibit families of cyclic circuits that are optimal in the number of gates, and we prove lower bounds on the size of equivalent acyclic circuits.
> we present theoretical justification for the claim that the optimal form of some [combinational] circuits requires cyclic topologies. We exhibit families of cyclic circuits that are optimal in the number of gates, and we prove lower bounds on the size of equivalent acyclic circuits.
http://www.mriedel.ece.umn.edu/wiki/images/7/7a/Riedel_Cycli...