@article{ritter_santos_tort_2001,  title={Vector Constants of Motion for Time-Dependent Kepler and Isotropic Harmonic Oscillator Potentials},  volume={31},  ISSN={0103-9733},  url={https://doi.org/10.1590/S0103-97332001000200024},  DOI={10.1590/S0103-97332001000200024},  number={2},  journal={Brazilian Journal of Physics},  publisher={Sociedade Brasileira de Física},  author={Ritter, O.M. and Santos, F.C. and Tort, A. C.},  year={2001},  month={Jun},  pages={304–307} }