@article{garcia_llibre_sotomayor_2006,  title={Lines of principal curvature on canal surfaces in R³},  volume={78},  ISSN={0001-3765},  url={https://doi.org/10.1590/S0001-37652006000300002},  DOI={10.1590/S0001-37652006000300002},  number={3},  journal={Anais da Academia Brasileira de Ciências},  publisher={Academia Brasileira de Ciências},  author={Garcia, Ronaldo and Llibre, Jaume and Sotomayor, Jorge},  year={2006},  month={Sep},  pages={405–415} }