Applying the correspondence principle to transform the wave function by a phase factor yields a constant phase gradient, implying an invariant electromagnetic field, a result which became a founding principle of quantum electrodynamics.
Majorana modified this equation by including the charge conjugate of the spin or wave function to describe neutrinos instead of electrons, which coincidentally also have spins of ½.  In Feynman slash notation, it can be summarized as "minus I times delta slash plus mass in brackets times U equals zero."  Applying the correspondence principle to transform the wave function by a phase factor yields a constant phase gradient, implying an invariant electromagnetic field, a result which became a founding principle of quantum electrodynamics. Any solution to this equation naturally solves the Klein-Fock-Gordon equation.  Predicting the existence of antiparticles four years before Carl Anderson discovered the positron, for 10 points, name this central wave equation of quantum field theory formulated by the 1932 Lucasian Chair in Cambridge and 1933 Nobel Prize winner in Physics.
Majorana modified this equation by including the charge conjugate of the spin or wave function to describe neutrinos instead of electrons, which coincidentally also have spins of ½.  
{Dirac} equation