1. The Thomas–Fermi-theory as result of a strong-coupling-limit;Baumgartner, Bernhard;Commun. Math. Phys.,1976
2. [BE11] Balinsky, Alexander A.; Evans, William D. Spectral Analysis of Relativistic Operators, World Scientific, 2011
3. Chapter 3;Bethe, Hans A.;Quantenmechanik der Ein-und Zwei-Elektronenatome,1933
4. The effect of relativity on atomic wave functions;Burke, V. M.;Proc. Phys. Soc.,1967
5. [Bha97] Bhatia, Rajendra Matrix Analysis, Graduate Texts in Mathematics, 169, Springer, 1997