@article{MZ_1970__117_171403,
     author = {Hartmut Ehlich and Werner Haussmann},
     title = {Cebysev-Approximation stegier {Fuktionen} in zwei {Ver\"anderlichen.}},
     journal = {Mathematische Zeitschrift},
     pages = {21--34},
     year = {1970},
     volume = {117},
     zbl = {0203.06601},
     url = {http://geodesic.mathdoc.fr/item/MZ_1970__117_171403/}
}