@article{MM2_1985__51_155073,
     author = {P.L. Butzer and W. Dickmeis},
     title = {On the {Sharpness} of {Non-Optimal} {Approximation} for {Semigroup} {Operators.}},
     journal = {Manuscripta mathematica},
     pages = {243--252},
     publisher = {mathdoc},
     volume = {51},
     year = {1985},
     zbl = {0583.41020},
     url = {http://geodesic.mathdoc.fr/item/MM2_1985__51_155073/}
}