@article{SF_1980__21_134451,
     author = {P.L. Butzer and L. Hahn},
     title = {A probabilistic approach to representation formulae for semigroups of operators with rates of convergence.},
     journal = {Semigroup forum},
     pages = {257--272},
     publisher = {mathdoc},
     volume = {21},
     year = {1980},
     zbl = {0452.60009},
     url = {http://geodesic.mathdoc.fr/item/SF_1980__21_134451/}
}