Singh, A., and K. C. Gupta. “Propagation of Discontinuities in A Non-Homogeneous Viscoelastic ROD With Varying Cross-Section”. The Journal of the Indian Mathematical Society, vol. 54, no. 1-4, Dec. 1989, pp. 165-8, https://informaticsjournals.co.in/index.php/jims/article/view/21888.