Even within the setting of edge-weighted labeled graphs that are equivalent to Lewis formulas there is no formal definition which graphs constitute viable molecules. 1H-azirene, for instance, is a perfectly ordinary graph, and the molecule it represents even has a chemical name. Nevertheless, 1H-azirene does not seem to exist. We therefore have to be consistent with operating on a space of labeled graphs that have an interpretation in chemistry. Moreover, the relationship of chemical graphs and molecules is not injective in general: tautomerism and mesomerism may lead to distinct graphs that represent the same molecule. These ambiguities are well known in the chemistry literature . They have very little impact on GA-based search, since the number of redundant representations usually is very small and the fitness evaluation can be performed for each of them independently.