1. A. A. Samarskii, The Theory of Difference Schemes [in Russian], Nauka, Moscow (1989).
2. O. Zenkevich and K. Morgan, Finite Elements and Approximation [Russian translation], Mir, Moscow (1986).
3. Z. C. Li, T. T. Lu, H. Y. Hu, and A. H.-D. Cheng, Trefftz and Collocation Methods, WIT Press, Cambridge (2008).
4. R. Piltner, Eng. Anal. Bound. Elem., 101, 102−112 (2019).
5. C.-S. Liu, F. Wang, and Y. Gu, Appl. Math. Lett., 87, 87−92 (2019).