@article{NUMA_1978__30_132553,
     author = {C. Zenger and H. Gietl},
     title = {Improved {Difference} {Schemes} for the {Dirichlet} {Problem} of {Poisson's} {Equation} in the {Neighbourhood} of {Corners.}},
     journal = {Numerische Mathematik},
     pages = {315--332},
     publisher = {mathdoc},
     volume = {30},
     year = {1978},
     zbl = {0425.65054},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1978__30_132553/}
}