With respect to model predictability testing at the RHS, in each complete reaction SMILES string in the test dataset, each product was hidden once alternatively with the missing molecule symbol "@@@". For example, a reaction with format of "A.B.C>>D.E" would be duplicated into two reaction SMILESs, "A.B.C>>@@@.E" and "A.B.C>>D.@@@". With respect to the LHS testing, in each reaction, each reactant was hidden once alternatively. The example reaction would be duplicated into three reaction SMILESs, "@@@.B.C>>D.E", "A.@@@.C>>D.E" and "A.B.@@@>>D.E". In this way, the number of reactions in the test dataset was also augmented, and the LHS ChemMLM and the RHS ChemMLM were used to predict the hidden molecules at each side respectively.