Konkol, F., and V. Kompis. “Trefftz Polynomials Reciprocity Based Boundary Element Formulations for Elastodynamics”. Computer Assisted Methods in Engineering and Science, vol. 11, no. 2-3, Jan. 2023, pp. 239-45, https://cames3.ippt.pan.pl/index.php/cames/article/view/1037.