Modeling the dynamics of tumor–immune cells interactions via fractional calculus Tao-Qian Tang, Zahir Shah, Rashid Jan and Ebraheem Alzahrani Eur. Phys. J. Plus, 137 3 (2022) 367 Published online: 19 March 2022 DOI: 10.1140/epjp/s13360-022-02591-0