“…It is known [20,24] that the spectrum of iH c on L 2 (−c, c) is the interval [−1, 1]. Fortunately, 1 is not in the point spectrum of iH c [10,33], thus allowing to invert (I − iH c ) in its range. Unfortunately, the range of (I − iH c ) is a dense proper subset of L 2 (−c, c) yielding an unstable inversion with the discretization schemes rendered ill-conditioned.…”