  The Bethe-Salpeter approach allows for quantum-field-theoretic descriptions
of relativistic bound states; its inherent complexity, however, usually
prevents to find its exact solutions. Under suitable simplifying assumptions
about the systems discussed, we derive analytically some examples of rigorous
solutions to the instantaneous homogeneous Bethe-Salpeter equation by relating
tentative solutions to the interactions responsible for the formation of bound
states.
