Identifying the optimal common subgraph is computationally intensive, making the MCS-based method less suitable for non-carbon compounds. Consequently, applying the two methods complementarily, each to their respective optimal scenarios, enhances Just like the rule-based method, the MCS-based method can only solve some imbalances. More precisely, the approach depends on the identification of the chemically correct MCS. The method outlined above, in particular, cannot handle rearrangement reactions or ring-formations. We shall return to this point in more detail, see Section 3.2 below. The MCS-based method also tends to fail if too many compounds or boundaries are found, the number of boundaries does not match, or the reaction is not carbon balanced afterwards, e.g., because not all carbon atoms in Y are covered by MCS matches. On the other hand, if a solution is found, the confidence is high that the result is in fact correct.