@article{1183523515,
author = {Butzer, P. L. and Tillmann, H. G.},
title = {An approximation theorem for semi-groups of operators},
journal = {Bull. Amer. Math. Soc.},
volume = {66},
number = {6},
year = {1960},
pages = { 191-193},
language = {en},
url = {http://dml.mathdoc.fr/item/1183523515}
}
Butzer, P. L.; Tillmann, H. G. An approximation theorem for semi-groups of operators. Bull. Amer. Math. Soc., Tome 66 (1960) no. 6, pp. 191-193. http://gdmltest.u-ga.fr/item/1183523515/