@article{NUMA_1963__5_131572,
     author = {N.J. LEHMANN},
     title = {Optimale {Eigenwerteinschlie{\ss}ungen.}},
     journal = {Numerische Mathematik},
     pages = {246--272},
     publisher = {mathdoc},
     volume = {5},
     year = {1963},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1963__5_131572/}
}