@article{NUMA_1972__19_132152,
     author = {K.P. Hadeler},
     title = {Bemerkung zu einer {Arbeit} von {W.} {Wetterling} \"uber positive {Operatoren.}},
     journal = {Numerische Mathematik},
     pages = {260--265},
     publisher = {mathdoc},
     volume = {19},
     year = {1972},
     zbl = {0225.65067},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1972__19_132152/}
}