@article{MZ_1986__192_173730,
     author = {K. H\"ollig and H.-O. Kreiss},
     title = {C?-Regularity for the {Porous} {Medium} {Equation.}},
     journal = {Mathematische Zeitschrift},
     pages = {217--224},
     publisher = {mathdoc},
     volume = {192},
     year = {1986},
     zbl = {0597.35107},
     url = {http://geodesic.mathdoc.fr/item/MZ_1986__192_173730/}
}