Gonska, H., and R. Păltănea. 2010. “Quantitative Convergence Theorems for a Class of Bernstein–Durrmeyer Operators Preserving Linear Functions”. Ukrains’kyi Matematychnyi Zhurnal 62 (7): 913–922. https://umj.imath.kiev.ua/index.php/umj/article/view/2924.