Rellich successfully worked on many partial differential equations with degeneracies. This accidental degeneracies are known as diabolic points. Differences among sequences are accounted for by using IUPAC degeneracies for individual bases. In this case, there are no degeneracies in the eigenspectrum. Again, observed degeneracies in the eigenspectrum are a consequence of discrete (or continuous) symmetries. The limiting cases, where one or several of these inequalities become equalities, are degeneracies.