Shobha Shukla, U. K. Shrivastav, and C. S. Rathore. “On the Approximation of Function by Product Means in the Holder Metric”. International Journal of Mathematics And Its Applications, vol. 5, no. 1 - C, Mar. 2017, pp. 343-8, https://ijmaa.in/index.php/ijmaa/article/view/782.