@article{GDZPPN002481421,
title = {On the Degree of Approximation by the Operators of de la Vall\'ee Poussin.},
journal = {Monatshefte f\"ur Mathematik},
volume = {87},
year = {1979},
pages = {53-64},
zbl = {0371.41010},
url = {http://dml.mathdoc.fr/item/GDZPPN002481421}
}
Schurer, F.; Steutel, F.W. On the Degree of Approximation by the Operators of de la Vallée Poussin.. Monatshefte für Mathematik, Tome 87 (1979) pp. 53-64. http://gdmltest.u-ga.fr/item/GDZPPN002481421/