The effect of normalization on the PFAS substructure search using Definition B (Figure ) on the CORE dataset is given in Table . The maximum number of unique PFAS compounds found by CDK and OCL using normalization is the same, i.e. 4,192 PFAS (according to Definition B). RDKit finds one structure less, which has a SMILES ClFC(F)C(F)(F)Cl (OCID190000011511). This compound structure is actually an incorrect representation of 1,2-dichlorotetrafluoroethane, containing a hypervalent fluorine (see Figure ). This structure was integrated into the OntoChem database of registered compounds when it was found in an early version of the Wikipedia Chemical infobox . Meanwhile, this entry has been corrected in Wikipedia Chemistry but still remains as a legacy in the OntoChem compound registry system, waiting for relinking to the correct structure and respective OCID190005899464.