Some remarks about intrinsic parity in Ryder's derivation of the Dirac   equation
  This work is a comment on Ryder's derivation of the Dirac equation, with emphasis on the physical contents of this equation: the notion of particles and antiparticles according to the Stueckelberg-Feynman interpretation, the opposite intrinsic parity between particles and antiparticles, and the spin. 
Fabian H. Gaioli and Edgardo T. Garcia Alvarez