The file reaction-isoxanzolines-2.xml in the supplementary material ZIP file shows a two-step reaction demonstrating the R-SPL capability of decomposing any action into sub-actions, in this case of "transforming" a reactant into the outcome of a preceding reaction. Since the product of the first reaction is the reactant of the second reaction, we do not need to repeat the definition of the substance when it repeats, instead, we assign an ID to it the first time and then we can reference it the second time through this ID.