1. Department of Theoretical Physics, Nuclear Physics Institute, Czech Academy of Sciences, Řež near Prague, Czechia
2. Doppler Institute for Mathematical Physics and Applied Mathematics, Czech Technical University, Prague, Czechia. E-mails: dittrich@ujf.cas.cz, exner@ujf.cas.cz
3. Institut für Numerische Mathematik, Technische Universität Graz, Graz, Austria. E-mail: kuehn@tugraz.at
4. Laboratoire de Mathématiques d’Orsay, Univ. Paris-Sud, CNRS, Université Paris-Saclay, Orsay, France. E-mail: konstantin.pankrashkin@math.u-psud.fr