  We prove almost optimal local well-posedness for the coupled
  Dirac-Klein-Gordon (DKG) system of equations in 1+3 dimensions.
  The proof relies on the null structure of the system, combined with bilinear
spacetime estimates of Klainerman-Machedon type.
  It has been known for some time that the Klein-Gordon part of the system has
a null structure; here we uncover an additional null structure in the Dirac
equation, which cannot be seen directly, but appears after a duality argument.
