Yukawa's approach and Dirac's approach to relativistic quantum mechanics

It is shown that Dirac's ''Poisson bracket'' approach to relativistic quantum mechanics is equivalent to the wave function approach which was originally suggested by Yukawa. It is pointed out that this circumstance is very similar to the case of nonrelativistic quantum mechanics in which Heisenberg's commutator formalism is equivalent to the algorithm based on the Schroedinger equation. (author)