In the parent scaffold generation routines (see below), only rings adhering to a set of criteria are considered for removal at the individual dissection steps. The first requirement is that a ring needs to be terminal, i.e. its removal must not result in a disconnected scaffold structure. This is checked internally by removing all atoms and bonds constituting the respective ring from the scaffold, discarding potential side chains that were connected to it, e.g. when the scaffold structural definition is used, and assessing whether the structure does not consist of multiple disconnected parts afterwards. If it does, the ring in question is not deemed terminal and hence not removable. This routine of checking for terminal rings has two major consequences: Internal rings that could be removed without resulting in a disconnected structure by turning some of their atoms and bonds into linker structures are still not considered terminal (Figure ). Secondly, the removal of rings from a scaffold cannot result in an artificially created spiro-ring system in Scaffold Generator (Figure ). Such cases are described in the original scaffold tree publication and the fifth prioritisation rule there is intended to prevent them if other rings can be removed first. But they are possible in general and would appear in a set of all possible parent scaffolds. Because the conversion of ring atoms to linker atoms and the artificial creation of spiro-ring systems are chemically nonintuitive when generating parent scaffolds, these possibilities have been excluded in Scaffold Generator. Another requirement to consider a ring for removal is that it must contain at least one atom that is not part of another ring as well. This criterion is adopted from the original scaffold tree publication . Here, the authors explain it with the example of adamantane. Using a ring detection algorithm that identifies the logical union of all SSSR in a structure, four rings are identified here and no atom is part of only one of them (compare Schuffenhauer et al. Scheme 2). Hence, the removal of one ring is not possible because its atoms and bonds that are part of other rings as well are generally preserved in the Scaffold Generator ring removal routines. Structures like adamantane are therefore not dissected at all.