Observing pulsars with f(R) gravity and using van der Waals equation of state in modelS. A. Mardan, A. Khalid, Rubab Manzoor and Muhammad Bilal RiazEur. Phys. J. Plus, 140 1 (2025) 30DOI: https://doi.org/10.1140/epjp/s13360-025-05976-z