@article{JRAM_1992__431_153451,
     author = {C. Hamburger},
     title = {Regularity of differential forms minimizing degenerate elliptic functionals.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {7--64},
     publisher = {mathdoc},
     volume = {431},
     year = {1992},
     zbl = {0776.35006},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1992__431_153451/}
}