A theoretically complete relativistic three-dimensional formalism was first derived from the Bethe-Salpeter equation by Lévy, Klein, and Macke. Two new derivations of this work are given with the aim of clarifying its close connection but nonidentity with various popular alternative formalisms of more recent vintage. Insofar as possible, the merits of the various formalisms are presented.
- Received 10 June 1974
- Published in the issue dated 15 December 1974
© 1974 The American Physical Society