The syntax changes introduced by DeepSMILES represent a subset of all the possible transformations that could be done. For example, consider how fundamental to an atom's identity is the number of heavy atom neighbours, or (almost) equivalently, the number of hydrogens attached. Yet, for atoms in the organic subset and particularly carbon, the relationship between this value and the characters in a SMILES string is non-trivial. However, if we treat the organic subset the same as other atoms, then the number of attached hydrogens would simply be listed for each atom. This may make it easier for DNNs to learn this syntax. In fact, if this were done and in addition we only allow atoms to have a fixed pre-defined valence, it is possible to achieve the parenthesis-free representation of a chemical structure described by Hiz and Eisman , which by definition does not allow unusual valences.