A more pronounced difference arises when there are extensive differences between systems, for example, as shown Fig. where free-base subporphyrin and H2[MO3] are demonstrated to form analogous sets of constitutional isomeric entities when analysed from a 𝒮 3 ℬ 2 partitioned perspective. Though these chemical systems are dramatically different, those parts of chemical space describing each of their 𝒮 3 ℬ 2 -partitioned constitutional changes have identical topologies; the shape of their respective chemical spaces are the same despite the idiosyncratic differences in energetics.