THORBERGSSON, G. Non-hyperbolic closed geodesics. MATHEMATICA SCANDINAVICA, [S. l.], v. 44, p. 135–148, 1979. DOI: 10.7146/math.scand.a-11799. Disponível em: https://www.mscand.dk/article/view/11799. Acesso em: 3 may. 2024.