A set of vertices in the modular product defines a feasible correspondence between bonds in the reactants and products if every pair of vertices is connected, i.e., all bond pairs are compatible with each other; this correspondence is one-to-one and does not contradict the principle of atom indivisibility. In graph theory, such a set of fully connected vertices is called a clique. As each vertex in a clique of the modular product represents the pair of identical bond between the reactants and products, the size of the clique equals the number of unchanged bonds. Since the MCESs maximize the number of unchanged bonds, the maximum cliques correspond to the MCESs. For instance, in Figure , the maximum clique of the modular product is {v 1 , v 4 , v 5 }, which corresponds to the The MCESs typically do not contain all atoms involved in the reaction, resulting in partial mappings between atoms in the reactants and products. These partial mappings can be completed by all possible permutations of the residual atoms for each element. In this way, we can compute all complete mappings through the maximum clique enumeration.