According to the Dirac conjecture, in the Hamiltonian and canonical formulation of gauge theory, the gauge transformations are generated by first class constraints. In the case of QED, the generator is the Gauss law operator.

According to the Dirac conjecture, in the Hamiltonian and canonical formulation of gauge theory, the gauge transformations are generated by first class constraints. In the case of QED, the gauge generator is the Gauss law operator ${\bf \nabla}\cdot {\bf E}-\frac{\rho}{\epsilon_0}$.