TUROVSKY, A. Expansion of the Two-particle Dirac Equation in Powers of 1/c to Higher Orders. Ukrainian Journal of Physics, [S. l.], v. 56, n. 1, p. 5, 2022. DOI: 10.15407/ujpe56.1.5. Disponível em: https://ujp.bitp.kiev.ua/index.php/ujp/article/view/2022149. Acesso em: 3 feb. 2023.