HANKEN, A. On the Origin of Four Pi in Physics. JOURNAL OF ADVANCES IN PHYSICS, [S. l.], v. 11, n. 9, p. 3994–4013, 2016. DOI: 10.24297/jap.v11i8.212. Disponível em: https://rajpub.com/index.php/jap/article/view/212. Acesso em: 14 may. 2025.