@article{article15f7d596,
title   = {Bifurcations of umbilic points and related principal cycles},
author = {Gutierrez, Carlos and Sotomayor, Jorge and Garcia, Ronaldo},
year = {2004},
doi = {10.1007/s10884-004-2783-9},
journal   = {Journal of Dynamics and Differential Equations}
}