On the Crucial Significance of the Multi-Configuration Structure of a   Bound State of Several Dirac Particles
  The structure of a bound state of several Dirac particles is discussed. Relying on solid mathematical arguments of the Wigner-Racah algebra, it is proved the a non-negligible number of configurations is required for a description of this kind of systems. At present, the main results are not widely known and this is the underlying reason for the phenomenon called the proton spin crisis. 
E. Comay
physics.gen-ph