All complete mappings obtained as AMM solutions contain some chemically equivalent mappings, which are generated by molecular symmetries in the reactants and products. Clustering these equivalent mappings by molecular symmetry yields chemically nonequivalent mappings that represent distinct reaction patterns. Our algorithm automatically clusters the complete mappings by molecular symmetry and returns a representative mapping from each cluster. (See Supporting Information for the mathematical details of the symmetry reduction method.) Figure shows an example of the symmetry reduction for a virtual reaction. In this reaction, there are six possible mappings, which are generated by atom label permutation: four with one bond cleavage and one bond formation, while two with two bond cleavages and two bond formations. The first four mappings correspond to the MCESs and are considered plausible. These mappings include equivalent mappings generated by the symmetric carbons 1 and 2 in the reactant. They can be classified into two nonequivalent reaction patterns: one via C-C bond cleavage and formation, and the other via C-O bond cleavage and formation. Therefore, the number of nonequivalent mappings in this case is two.