  In 1929 Lanczos showed how to derive Dirac's equation from a more fundamental
system that predicted that spin 1/2 particles should come in pairs. Today,
these pairs can unambiguously be interpreted as isospin doublets. From the same
fundamental equation, Lanczos derived also the correct form of the wave
equation of massive spin 1 particles that would be rediscovered in 1936 by
Proca.
  Lanczos's fundamental system was put in Lagrangian form and generalized in
1933 by Einstein and Mayer, who used the semivector instead of the quaternion
formalism. Although they not did study all possible solutions, Einstein and
Mayer showed that the doublets consisted of particles with different mass and
charge. In fact, there are two main classes of doublets: proton/neutron and
electron/neutrino pairs.
