@article{NUMA_1979__32_132595,
     author = {W. Hackbusch},
     title = {On the {Fast} {Solutions} of {Nonlinear} {Elliptic} {Equations.}},
     journal = {Numerische Mathematik},
     pages = {83--96},
     publisher = {mathdoc},
     volume = {32},
     year = {1979},
     zbl = {0386.65047},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1979__32_132595/}
}