LARMORE, L. L.; THOMAS, E. Group Extensions and Principal Fibrations. MATHEMATICA SCANDINAVICA, [S. l.], v. 30, p. 227–248, 1972. DOI: 10.7146/math.scand.a-11078. Disponível em: https://www.mscand.dk/article/view/11078. Acesso em: 28 apr. 2024.