Semirelativistic Treatment of Bound States
  This talk reviews several aspects of the "semirelativistic" description of bound states by the spinless Salpeter equation (which represents the simplest equation of motion incorporating relativistic effects) and, in particular, presents or recalls some very simple and elementary methods which allow to derive rigorous statements on the corresponding solutions, that is, on energy levels as well as wave functions. In principle, these methods work for all physical situations which may be formulated as an eigenvalue problem. 
Wolfgang Lucha and F. F. Schoberl