C.-Y. Lee, Q.-H. Qin, and H. Wang, “Trefftz functions and application to 3D elasticity”, Comp. Assist. Methods Eng. Sci., vol. 15, no. 3-4, pp. 251–263, Dec. 2008, Accessed: Mar. 05, 2026. [Online]. Available: https://cames.ippt.gov.pl/index.php/cames/article/view/734