If a center passes Rule 4b undecided, it means that there are only three possibilities: (1) There is no ligand chirality; (2) two or more ligands have identical chirality descriptors; or (3) the two ligands each have sub-branches with opposite chirality. Rule 4c takes care of case ( ), where we assign r over s, and m over p. The implementation of Rule 4c is a straightforward extension of the implementation of Rule 4a.