Mustăţa, Costică. “On a Problem of B.A. Karpilovskaja”. Rev. Anal. Numér. Théor. Approx. 28, no. 2 (August 1, 1999): 179–189. Accessed April 8, 2025. https://ictp.acad.ro/jnaat/journal/article/view/1999-vol28-no2-art8.