proving Bargmann's limit. Note that as the integral on the right is assumed to be finite, so must be N and N ℓ ℓ . Furthermore, for a given value of ℓ ℓ , one can always construct a potential V ℓ ℓ for which N ℓ ℓ is arbitrarily close to Bargmann's limit. The idea to obtain such a potential, is to approximate Dirac delta function potentials, as these attain the limit exactly. An example of such a construction can be found in Bargmann's original paper.