“…When α 2 l 2 = 1, the limit µ → 0 can be taken smoothly in the coordinatesr = γr,t = t/γ in which the solution becomes The charge differences between a given solution (g µν , A µ ) and an infinitesimally close one (g µν + δg µν , A µ + δA µ ) are controlled by the linearized theory around (g µν , A µ ). The equivalence classes of conserved n− 2-forms (here 1-forms) of the linearized theory can be shown [26,27] to be in one-to-one correspondence with gauge parameters (ξ µ , ǫ) satisfying…”