@article{10_4153_CJM_1977_081_6,
     author = {Butzer, P. L. and Dyckhoff, H. and G\"orlich, E. and Stens, R. L.},
     title = {Best {Trigonometric} {Approximation,} {Fractional} {Order} {Derivatives} and {Lipschitz} {Classes}},
     journal = {Canadian journal of mathematics},
     pages = {781--793},
     year = {1977},
     volume = {29},
     number = {4},
     doi = {10.4153/CJM-1977-081-6},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1977-081-6/}
}