@article{JRAM_1979__309_152147,
     author = {S. Hildebrandt and K.-O. Widman},
     title = {Variational inequalities for vector-valued functions.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {191--220},
     publisher = {mathdoc},
     volume = {309},
     year = {1979},
     zbl = {0408.49012},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1979__309_152147/}
}