Consider reaction 1 from the WCCR10 40 set as shown in Fig. . In this case, the transition metal is unique and is not contained in any set. Then, the set S 1 of nitrogen atoms has the closest distance to the transition metal and is therefore prioritized over the sets S 2 and S 3 of neighboring carbon atoms which are in turn prioritized over the set S 4 of carbon atoms in the methyl groups.