“Existence of Solutions and Hyers-Ulam Stability for a Coupled System of Nonlinear Langevin Equations Involving φ-Riemann-Liouville and ψ-Caputo Fractional Derivatives Subject to Mixed Boundary Conditions”. Gulf Journal of Mathematics 20, no. 2 (August 18, 2025): 489–508. Accessed September 22, 2026. https://gjom.org/index.php/gjom/article/view/3279.