Redundant poles of the S-matrix for the one-dimensional Morse potential M. Gadella, A. Hernández-Ortega, Ş. Kuru and J. Negro Eur. Phys. J. Plus, 135 10 (2020) 822 Published online: 13 October 2020 DOI: 10.1140/epjp/s13360-020-00833-7