Diabolical points and Rayleigh-wave propagation

Eigenvalue problems with “peculiar properties” were studied in a famous paper by von Neumann and Wigner. The phenomenon of diabolical points is placed into an extended context and is connected for the first time with Rayleigh-wave propagation. The associated appearance of osculation, avoided crossing or repulsion is discussed by using simple models. Everything is connected with everything. Alexander von Humboldt (1769-1859)