Gonska, Heinz H. “On Approximation by Linear Operators: Improved Estimates”. Anal. Numér. Théor. Approx. 14, no. 1 (February 1, 1985): 7–32. Accessed November 26, 2024. https://ictp.acad.ro/jnaat/journal/article/view/1985-vol14-no1-art2.