A _ → A _ + ∇ _ . χ ϕ → ϕ − 1 c ∂ t χ {\displaystyle {\begin{aligned}&{\underline {A}}\to {\underline {A}}+{\underline {\nabla }}.\chi \\&\phi \to \phi -{\frac {1}{c}}{{\partial }_{t}}\chi \\\end{aligned}}} [Category:Elektrodynamik]
