When transforming ring closure symbols with DeepSMILES, we replace the two ring closure symbols in a pair with a single one, at the location of the second symbol. One may ask why not replace the first symbol instead? The reason is related to the tree structure of a SMILES string; for any node in a tree, there is only a single path leading to it from the root but thereafter the path may split multiple times. Thus, while one can refer to the atom that appeared five bonds earlier (along the path leading to this atom), there may be multiple candidates for the atom that appears five bonds later.