M. Al-Mekhlafi, S., Boudaoui, A., Laksaci, N., Abdeljawad, T., & Abdalla, B. (2026). Modeling Dengue-COVID-19 Co-Epidemics via Crossover Discrete Time Systems with Variable-Order Fractional Memory. Contemporary Mathematics, 7(4), 4111–4162. https://doi.org/10.37256/cm.7420268949