Kostova, V. A. (1990). An exact estimate for the approximation of the function Msgn(A-X) with Bernstein polynomials in Hausdorff metric. Anal. Numér. Théor. Approx., 19(2), 143-150. https://ictp.acad.ro/jnaat/journal/article/view/1990-vol19-no2-art8