Question

What is the name of the formula on the picture Electron (painting from the Hungarian painter Oliver Sin)?

Answer 1

?

Answer 2

On the left hand side is energy minus rest energy, written according to special relativity. On the right side, I'm not sure, it looks a little like an operator for the potential energy, particularly given the e there.

My first guess is that it might be some fragment of equation from the first attempts to write a relativistic theory of the electron, before the Dirac equation. That's because of the line drawn through the formula, as if it was found to be wrong and discarded.