In some cases, we have observed that the head-and-tail assignment is correct but the sanitization of the SMILES structure is incorrect, in particular if a ring-opening process is involved. We show the example of poly(3-hydroxybutyrate) polymer with its heterocycle precursor in Fig. ). The head and tail positions were correctly assigned to the oxygen atom of the oxetane ring and to the carbon atom of the carbonyl group. However, the ring-opening process performed by the HTA algorithm generated an incorrect SMILES that cannot be visualized.