@article{drigo filho_ricotta_2001,  title={The Hierarchy of Hamiltonians for a Restricted Class of Natanzon Potentials},  volume={31},  ISSN={0103-9733},  url={https://doi.org/10.1590/S0103-97332001000200029},  DOI={10.1590/S0103-97332001000200029},  number={2},  journal={Brazilian Journal of Physics},  publisher={Sociedade Brasileira de Física},  author={Drigo Filho, Elso and Ricotta, Regina Maria},  year={2001},  month={Jun},  pages={334–339} }