The conversion of two ring closure symbols to a single one addresses the difficulty of generating SMILES strings with matching ring closure digits. However, we believe that this syntax has additional benefits for its application to deep neural nets. Consider that a phenyl ring may be indicated in a SMILES string by a mixture of "c1…..c1", "c2……c2", "c3……c3", and so on, with frequencies that differ along the length of a SMILES string. (As an aside, these frequencies will differ between programs as some reuse ring closure digits as soon as possible, while others may only do so as soon as digit 9 is reached.) In contrast, a phenyl ring will always be present as "c6" in DeepSMILES.