Nudel’man, M. A. 2005. “On Initial Data of a Simple Conservative Scattering System That Can Be Transferred to Zero by a Sequence of Inputs from <i>l </I&gt;²”. Ukrains’kyi Matematychnyi Zhurnal 57 (4), 559–563. https://umj.imath.kiev.ua/index.php/umj/article/view/3621.