Parasidis, I.N., and E. Providas. “Factorization Method for Solving Nonlocal Boundary Value Problems in Banach Space”. Bulletin of the Karaganda University. Mathematics Series 103, no. 3 (September 30, 2021): 76–86. Accessed August 24, 2025. http://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/465.