@article{MZ_1976__149_172381,
     author = {Emanuel jr. Sperner},
     title = {Ein {Regularit\"atssatz} f\"ur {Systeme} nichtlinearer elliptischer {Differentialgleichungen.}},
     journal = {Mathematische Zeitschrift},
     pages = {57--68},
     publisher = {mathdoc},
     volume = {149},
     year = {1976},
     zbl = {0319.35037},
     url = {http://geodesic.mathdoc.fr/item/MZ_1976__149_172381/}
}