Ulam–Hyers–Rassias Stability of ψ-Hilfer Volterra Integro-Differential Equations of Fractional Order Containing Multiple Variable Delays

The authors consider a nonlinear ψ-Hilfer fractional-order Volterra integro-differential equation (ψ-Hilfer FrOVIDE) that incorporates N-multiple variable time delays into the equation. By utilizing the ψ-Hilfer fractional derivative, they investigate the Ulam–Hyers–Rassias and Ulam–Hyers stability of the equation by using fixed-point methods. Their results improve existing ones both with and without delays by extending them to nonlinear ψ-Hilfer FrOVIDEs that incorporate N-multiple variable time delays.