For instance, ids 82, 63, 50, and 24, ranked respectively 3, 4, 8 and 9, are compounds that all three tools were, unfortunately, unable to correctly annotate. This illustrates that our function k is designed as an assistance to an expert and not as a substitute. As an additional comment on MS2DECIDE's ranking, it appears that compounds belonging to phytochemical groups that are important in terms of number of representatives (e.g. flavonoids kaempferol id 56 and hyperoside id 47) tend to be easily identified as known compounds. It can be supposed that spectrometric data related to close analogues of such molecules are more likely to have been uploaded in publicly available spectral repositories by comparison to structures pertaining to minor natural product classes such as cynodine (id 24) and isoelaiocaprine (id 50). In the meantime, it must be stressed out that MS2DECIDE was able to rank some compounds in the end of the list despite the latter not belonging to rich classes of natural products (e.g., eserine (id 32) and pilocarpine (id 71)). Nevertheless, both these compounds are endowed with significant bioactivities and have been used in pharmacy.