THORBERGSSON, Gudlaugur. Non-hyperbolic closed geodesics. Mathematica Scandinavica, Berkeley, CA, United States, v. 44, p. 135–148, 1979. DOI: 10.7146/math.scand.a-11799. Disponível em: https://journals.msp.org/mscand/article/view/1850. Acesso em: 25 jul. 2026.