[1] Becker, M., Kucharski, D., Nessel, R. J.: Global approximation theorems for the Szasz-Mirakjan operators in exponential weight spaces. In: Linear Spaces and Approximation (Proc. Conf. Oberwolfach, 1977), Birkhäuser Verlag, Basel ISNM, 40 (1978), 319-333. MR 0499919

[2] Totik, V.: Uniform approximation by Szasz-Mirakyan type operators. Acta Math. Hung. 41, 3-4 (1983), 291-307. MR 0703742

[3] Z. Walczak: Approximation properties of certain linear positive operators in exponential weighted spaces. Acta Univ. Palacki. Olomuc., Fac. rer. nat., Math. 42 (2003), 123-130. MR 2056027 | Zbl 1054.41015