@article{10_4064_ap_23_1_41_48,
     author = {S. Bal},
     title = {Smoothness of solutions for a system of first order non-linear partial differential equations},
     journal = {Annales Polonici Mathematici},
     pages = {41--48},
     publisher = {mathdoc},
     volume = {23},
     number = {1},
     year = {1970},
     doi = {10.4064/ap-23-1-41-48},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-23-1-41-48/}
}