Kostova, V. At. “Approximation of Bounded Non-Negative Functions by Polynomials With Positive Coefficients in the Hausdorff Metric”. Anal. Numér. Théor. Approx. 18, no. 1 (February 1, 1989): 67–72. Accessed September 3, 2025. https://www.ictp.acad.ro/jnaat/journal/article/view/1989-vol18-no1-art8.