Mentynskyi, S. M. “Two-Sided Approximation of Solutions of a Multipoint Problem for an Ordinary Differential Equation With Parameters”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 57, no. 1, Jan. 2005, pp. 125–130, https://umj.imath.kiev.ua/index.php/umj/article/view/3579.