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