@article{CMJ_2007__57_1_a8,
     author = {S\'aez, Eduardo and Stange, Eduardo and Sz\'ant\'o, Iv\'an},
     title = {Coexistence of small and large amplitude limit cycles of polynomial differential systems of degree four},
     journal = {Czechoslovak Mathematical Journal},
     pages = {105--114},
     publisher = {mathdoc},
     volume = {57},
     number = {1},
     year = {2007},
     mrnumber = {2309952},
     zbl = {1168.92319},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMJ_2007__57_1_a8/}
}