Srivastava, K. B., & Saxena, R. (1981). On interpolation operators - III (A proof of Telyakovskii-Gopengauz’s theorem for differentiable functions). Anal. Numér. Théor. Approx., 10(2), 247–262. Retrieved from https://ictp.acad.ro/jnaat/journal/article/view/1981-vol10-no2-art15