In the modern literature the Feynman path integral , for the Dirac equation is written such as presented below. Generally speaking, the form that is employed for the Dirac equation is [1, eq 1.2 page 64], iℏ ∂ ∂t u(t, x) = Hu(t, x). The u in is an N × 1 vector. Here we will take N=4. In ,