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, [S. l.], v. 20, n. 2, p. 489–508, 2025. DOI: 10.56947/gjom.v20i2.3279. Disponível em: https://www.gjom.org/index.php/gjom/article/view/3279. Acesso em: 21 aug. 2026.