Srivastava, K. B., & Saxena, R. B. (1985). On interpolation operators - IV (Estimates in the neighbourhood of nodal points for differentiable functions). Anal. Numér. Théor. Approx., 14(2), 137–145. Retrieved from https://ictp.acad.ro/jnaat/journal/article/view/1985-vol14-no2-art7