A partitioned CRS. A partitioned CRS within the binary polymer model. One set of molecules is built from the ‘square’ and ‘circle’ monomers, and the other is built from the ‘triangle’ and ‘hexagon’ monomers. The molecules at the bottom of the image comprise the food set and give rise to the other molecules via the ligation and cleavage reactions r1,…,R4. Dashed arrows indicate which molecules catalyse which reactions. In this case, the entire CRS is an RAF. Note that while there is intra- and inter-modular catalysis, there are no reactions involving molecules from both modules. This is emphasized by the enclosure of each module within a large circle: of course, in real systems, the molecules would be free to mingle.