HONG, Xiao. The 2-Sheeted, 3-Sheeted, and Universal Coverings of Corresponding 2-Oriented Graph of Rank-2 Free Group. Science and Technology of Engineering, Chemistry and Environmental Protection, [S. l.], v. 2, n. 6, p. 5992, 2024. DOI: 10.61173/0recy351. Disponível em: https://stecep.deanfrancis.press/article/view/1177. Acesso em: 4 nov. 2026.