L = i Ψ ¯ γ μ ∂ μ Ψ − Ψ ¯ Ψ − q Ψ ¯ γ 0 Ψ Φ + 1 2 ( ∂ μ Φ ) ( ∂ μ Φ ) {\it L}=i\bar{\Psi}{\gamma}^{\mu}{\partial}_{\mu}{\Psi}-\bar{\Psi}{\Psi}-q\bar{\Psi}{\gamma}^{0}{\Psi}\Phi+{1\over 2}({\partial}_{\mu}\Phi)({\partial}^{\mu}\Phi)