Selmani M, Harrat C, Bouizem Y. Existence, Uniqueness, and Stability of Solutions to the Langevin Equation via the $(k,\psi)$-Hilfer Proportional Fractional Operator with Multi-Point Fractional Boundary Conditions. DNC. 2026;15(4):491-507. doi:10.5890/DNC.2026.12.002