We start with the message, update, and readout functions used by St. John et al. The initial features of the atoms and bonds are determined by looking up a set of features for each type of atom-defined using its element, number of bonds, number of bonded hydrogen atoms, and whether it is aromatic-and for each bond-defined using its type (e.g., single vs. double), whether the bond is conjugated or in a ring, and the elements of the bonded atoms.