Editing Quantum electrodynamics (section)

===Propagators===
Finally, one has to compute ''P''(''A'' to ''B'') and ''E''(''C'' to ''D'') corresponding to the probability amplitudes for the photon and the electron respectively. These are essentially the solutions of the [[Dirac equation]], which describe the behavior of the electron's probability amplitude and the [[Maxwell's equations]], which describes the behavior of the photon's probability amplitude. These are called [[Propagator|Feynman propagators]]. The translation to a notation commonly used in the standard literature is as follows:

:<math>P(A \text{ to } B) \to D_F(x_B - x_A),\quad  E(C \text{ to } D) \to S_F(x_D - x_C),</math>

where a shorthand symbol such as <math>x_A</math> stands for the four real numbers that give the time and position in three dimensions of the point labeled ''A''.