reference types (Section 2.1.1). A total score of 100% corresponds to patterns matching all reference atom or fragment types and would indicate complete success for a set of working atom or fragment types. However, it is not necessary that we exactly reproduce the atom typing or fragment typing of existing force fields to succeed, especially in view of the combinatorial challenge we face; it is sufficient that we sample comparable chemical complexity. Thus, achieving a high total score on average would also be acceptable, especially if we can achieve at the same time a partial score of 100% for most atom or fragment types. That is, for both SMARTY and SMIRKY, we seek to recover SMARTS or SMIRKS which will mirror the previously defined indirect or direct chemical perception from the reference force field, by separating atoms or fragments into similar types. However, the automatically generated trees do not necessarily need to encode the exact same chemical perception trees as those from the reference force field.