Saxena, R. B., and K. B. Srivastava. “On Interpolation Operators (I) (A Proof of Jakson’s Theorem for Differentiable Functions)”. Anal. Numér. Théor. Approx. 7, no. 2 (August 1, 1978): 211–223. Accessed May 8, 2024. https://ictp.acad.ro/jnaat/journal/article/view/1978-vol7-no2-art10.