1. u. , Methods of Mathematical Physics, Vol. 1, Interscience Publ. Inc., New York 1953, S. 48.
2. Delta‐Function Model. I. Electronic Energies of Hydrogen‐Like Atoms and Diatomic Molecules
3. Vorlesungen über Variationsrechnung, Koehler & Amelang, Leipzig 1949 S. 25/26.
4. On the variational method of the nonrelativistic scattering
5. The Calculation of Atomic Structures, John Wiley Sons, Inc., New York 1957, S. 25.