@article{JDM_1967__70_146562,
     author = {P.L. Butzer and K. Scherer and R.J. Nessel},
     title = {Trigonometric {Convolution} {Operators} with {Kernels} having {Alternating} {Signs} and their {Degree} of {Convergence.}},
     journal = {Jahresbericht der Deutschen Mathematiker-Vereinigung},
     pages = {86--99},
     publisher = {mathdoc},
     volume = {70},
     year = {1967},
     zbl = {0177.31201},
     url = {http://geodesic.mathdoc.fr/item/JDM_1967__70_146562/}
}