@article{EJDE_2006__2006__a41,
     author = {Cuoghi,  Paola and Salani,  Paolo},
     title = {Convexity of level sets for solutions to nonlinear elliptic problems in convex rings},
     journal = {Electronic journal of differential equations},
     year = {2006},
     volume = {2006},
     zbl = {1128.35320},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2006__2006__a41/}
}