@article{RLIN_2004_9_15_1_a1,
     author = {Guti\'errez, Cristian E. and Lanconelli, Ermanno},
     title = {Classical, viscosity and average solutions for {PDE{\textquoteright}s} with nonnegative characteristic form},
     journal = {Atti della Accademia nazionale dei Lincei. Rendiconti Lincei. Matematica e applicazioni},
     pages = {17--28},
     publisher = {mathdoc},
     volume = {Ser. 9, 15},
     number = {1},
     year = {2004},
     zbl = {1098.35052},
     mrnumber = {262881},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RLIN_2004_9_15_1_a1/}
}