@article{MZ_1977__156_172586,
     author = {Emanuel jr. Sperner},
     title = {\"Uber eine scharfe {Schranke} in der {Regularit\"atstheorie} elliptischer {Systeme.}},
     journal = {Mathematische Zeitschrift},
     pages = {255--264},
     publisher = {mathdoc},
     volume = {156},
     year = {1977},
     zbl = {0363.35012},
     url = {http://geodesic.mathdoc.fr/item/MZ_1977__156_172586/}
}