Li , Xinchun. (2017). $ℓ^1$-Error Estimates on the Hamiltonian-Preserving Scheme for the Liouville Equation with Piecewise Constant Potentials: A Simple Proof.
            <i>Journal of Computational Mathematics</i>. <i>35</i> (6).
            814-827.
         doi:10.4208/jcm.1701-m2016-0717