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@article{MOMA_1979__87_177903, author = {F. Schurer and F.W. Steutel}, title = {On the {Degree} of {Approximation} by the {Operators} of de la {Vall\'ee} {Poussin.}}, journal = {Monatshefte f\"ur Mathematik}, pages = {53--64}, publisher = {mathdoc}, volume = {87}, year = {1979}, zbl = {0371.41010}, url = {http://geodesic.mathdoc.fr/item/MOMA_1979__87_177903/} }
F. Schurer; F.W. Steutel. On the Degree of Approximation by the Operators of de la Vallée Poussin.. Monatshefte für Mathematik, Tome 87 (1979), pp. 53-64. http://geodesic.mathdoc.fr/item/MOMA_1979__87_177903/