@article{NUMA_1968__11_131833,
     author = {J. NITSCHE},
     title = {Ein {Kriterium} f\"ur die {Quasi-Optimalit\"at} des {Ritzschen} {Verfahrens.}},
     journal = {Numerische Mathematik},
     pages = {346--348},
     publisher = {mathdoc},
     volume = {11},
     year = {1968},
     zbl = {0175.45801},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1968__11_131833/}
}