@article{NUMA_1970__15_131979,
     author = {W. WETTERLING},
     title = {Definitheitsbedingungen f\"ur relative {Extrema} bei {Optimierungs-} und {Approximationsaufgaben.}},
     journal = {Numerische Mathematik},
     pages = {122--136},
     publisher = {mathdoc},
     volume = {15},
     year = {1970},
     zbl = {0184.39101},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1970__15_131979/}
}