)We can also suppress states that lie inside the image of "QB" when defining the asymptotic states of our theory—but the reasoning is a bit subtler.Since we have postulated that the "true" Lagrangian of our theory is gauge invariant, the true "states" of our Hamiltonian system are equivalence classes under local gauge transformation; in other words, two initial or final states in the Hamiltonian picture that differ only by a BRST exact state are physically equivalent.