@article{ARM_1998__34_1_a13,
     author = {Kratz, Werner},
     title = {Quadratic functionals: positivity, oscillation, {Rayleigh's} principle},
     journal = {Archivum mathematicum},
     pages = {143--151},
     publisher = {mathdoc},
     volume = {34},
     number = {1},
     year = {1998},
     mrnumber = {1629688},
     zbl = {0921.49025},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ARM_1998__34_1_a13/}
}