In particular, we have not investigated here how mutation and recombination operators interact. We expect that suitably designed mutation procedures can replace the reservoir sets of structural building blocks used as technical device in proving the reachability results. Moreover, chirality is an important feature of molecules that is not represented at the level of chemical (multi)graphs. These can thus be seen as representing the equivalence class of all stereo-isomers. In a brute-force manner, these can then be enumerated, see e.g. . A more elegant approach would be to make use of annotation of stereochemical information which may be specified by structural formulas.