The closest chemical equivalent to the simple string search example is locating a predefined molecule in chemical space, i.e. rediscovery. Rediscovery, using text strings (SMILES, DeepSMILES, and SELF-IES) to represent the molecules, is shown to be significantly more challenging even though the mechanics of the GA search (i.e. the mating and mutation operations) are very similar. Most string-based searches fail to find the target after 100,000 molecule evaluations starting from initial populations made by prescreening over 1.6 million molecules (Figure ). The primary difference between the simple phrase search and rediscovery is that in the latter case the score can only be evaluated for strings that correspond to valid molecules, while in the former case all strings can be scored. Since most string-based mating a mutation operations lead to strings with invalid syntax and zero scores for the rediscovery search, there are many fewer paths leading to the target (Figure ) compared to the simple string search.