@article{10_4064_cm113_1_10,
     author = {Doan The Hieu and Tran Le Nam},
     title = {On the four vertex theorem in planes with
 radial density $e^{\varphi(r)}$},
     journal = {Colloquium Mathematicum},
     pages = {169--174},
     publisher = {mathdoc},
     volume = {113},
     number = {1},
     year = {2008},
     doi = {10.4064/cm113-1-10},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm113-1-10/}
}