@article{articleacf8476b,
title   = {Umbilic and tangential singularities on configurations of principal curvature lines},
author = {Garcia, Ronaldo Alves and Sotomayor, Jorge},
year = {2002},
doi = {10.1590/S0001-37652002000100001},
journal   = {Anais da Academia Brasileira de Ciências}
}