@article{10_4153_CMB_1993_036_x,
     author = {Urbina, A.M.},
     title = {Limit {Cycles} of {Li\'enard} {Equations} {With} {Non} {Linear} {Damping}},
     journal = {Canadian mathematical bulletin},
     pages = {251--256},
     year = {1993},
     volume = {36},
     number = {2},
     doi = {10.4153/CMB-1993-036-x},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1993-036-x/}
}