Almost convexity and quantitative Korovkin type results
\textit{O. Shisha} and \textit{B. Mond} [Proc. Natl. Acad. Sci. USA 60, 1196-1200 (1968; Zbl 0164.07102)] and \textit{H.-B. Knoop} and \textit{P. Pottinger} [Math. Z. 148, 23-32 (1976; Zbl 0322.41016)] investigated the approximation of the \(k\)-th derivative of a function by means of linear operators under various assumptions related to shape preserving properties. Their results are discussed in this paper and new estimates are given for operators which have more interesting shape preserving properties.
scientific article; zbMATH DE number 1369532