BENSLIMANE, S. et al. 2023. Expansion-compression fixed point theorem of Leggett-Williams type for the sum of two operators and applications for some classes of BVPs. Studia Universitatis Babeș-Bolyai Mathematica. 68, 3 (Sep. 2023), 631–647. DOI:https://doi.org/10.24193/subbmath.2023.3.12.