Nonlocal symmetries and new interaction waves of the variable-coefficient modified Korteweg–de Vries equation in fluid-filled elastic tubesJian-Wen Wu, Jun-Tao He and Ji LinEur. Phys. J. Plus, 137 7 (2022) 814DOI: https://doi.org/10.1140/epjp/s13360-022-03033-7