Perestyuk, N. A., and A. M. Ronto. 1995. “On a Method for Construction of Successive Approximations for Investigation of Multipoint Boundary-Value Problems”.
Ukrains’kyi Matematychnyi Zhurnal 47 (9): 1243–1253.
https://umj.imath.kiev.ua/index.php/umj/article/view/5524.