Approximation of differentiable functions by polynomial splines in domains with external peaks

Semenyuk, V. B. “Approximation of Differentiable Functions by Polynomial Splines in Domains With External Peaks”. Ukrains’kyi Matematychnyi Zhurnal, vol. 46, no. 9, Sept. 1994, pp. 1224–1233, https://umj.imath.kiev.ua/index.php/umj/article/view/5639.