Novikov, S. I. “Approximation of One Class of Differentiable Functions by Piecewise-Hermitian<em class="a-Plus-plus">L</Em&gt;-Splines”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 51, no. 11, Nov. 1999, pp. 1495–1504, https://umj.imath.kiev.ua/index.php/umj/article/view/4751.