PRECUM, R. (2016) “Abstract method of upper and lower solutions and application to singular boundary value problems: Dedicated to Professor Ioan A. Rus on the occasion of his 80th anniversary”, Studia Universitatis Babeș-Bolyai Mathematica, 61(4), pp. 443–451. Available at: https://studia.reviste.ubbcluj.ro/index.php/subbmathematica/article/view/5636 (Accessed: 5 February 2025).