Knoop, Hans-Bernd, and Xinlong Zhou. “Inequalities for Some Iterated Linear Operators and Their Applications in Approximation Theory”. Rev. Anal. Numér. Théor. Approx. 30, no. 2 (August 1, 2001): 197–206. Accessed May 12, 2024. https://ictp.acad.ro/jnaat/journal/article/view/2001-vol30-no2-art7.