@article{MZ_1973__131_171893,
     author = {Stefan Hildebrandt},
     title = {Interior {C1} + {...-Regularity} of {Solutions} of {Two-Dimesional} {Variational} {Problems} with {Obstacles.}},
     journal = {Mathematische Zeitschrift},
     pages = {233--240},
     publisher = {mathdoc},
     volume = {131},
     year = {1973},
     zbl = {0275.49007},
     url = {http://geodesic.mathdoc.fr/item/MZ_1973__131_171893/}
}