@article{EJDE_2015__2015__a41,
     author = {Sabina de Lis,  Jose C.},
     title = {Hopf maximum principle revisited},
     journal = {Electronic journal of differential equations},
     year = {2015},
     volume = {2015},
     zbl = {1331.35065},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2015__2015__a41/}
}