Altomare, Francesco, and Ioan Raşa. “Approximation by Positive Operators in the Space \(C^{(p)}([a,b])\)”. Anal. Numér. Théor. Approx. 18, no. 1 (February 1, 1989): 1–11. Accessed April 14, 2025. https://ictp.acad.ro/jnaat/journal/article/view/1989-vol18-no1-art1.