@article{JRAM_1997__485_183541,
     author = {David Preiss},
     title = {Additional regularity for {Lipschitz} solutions of {PDE.}},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {197--208},
     publisher = {mathdoc},
     volume = {485},
     year = {1997},
     zbl = {0870.35022},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1997__485_183541/}
}