$$^\prime\!\!\!\!\boldsymbol{\partial}\boldsymbol{\partial}$$ $$\left(\; i\, \partial \hspace{-0.5em} / - m \;\right)\psi = 0 \\\left(\; i\, /\!\!\!\partial - m \;\right)\psi = 0 $$ $$\boldsymbol{\eth}$$ $$\eth$$ $$\varrho$$ $$\boldsymbol{\varrho}$$
