 In order to do so, BLW propose a distance function \(D\) between probability distributions, such that \(D(\mu, \mu')\) tells us how close the marginal position distribution \(\mu'(q)\) for the unsharp position \(Q'\) is to the exact distribution \(\mu(q)\) in a sharp position measurement, and likewise, \(D(\nu ,\nu')\) tells us how close the marginal momentum distribution \(\nu'(p)\) for \(P'\) is to the the exact momentum distribution \(\nu(p)\).