Bound States by the Spinless Salpeter Equation
  In quantum theory, bound states are described by eigenvalue equations, which usually cannot be solved exactly. However, some simple general theorems allow to derive rigorous statements about the corresponding solutions, that is, energy levels and wave functions. These theorems are applied to the prototype of all relativistic wave equations, the spinless Salpeter equation. 
Wolfgang Lucha and F. F. Schoberl