@article{articlef3f3e8dc,
title   = {More limit cycles than expected in Liénard equations},
author = {Dumortier, Freddy and Panazzolo, Daniel and Roussarie, Robert},
year = {2007},
doi = {10.1090/s0002-9939-07-08688-1},
journal   = {Proceedings of the American Mathematical Society}
}