BUNDSCHUH, P. Irrationalität und Transzendenz gewisser Reihen. MATHEMATICA SCANDINAVICA, [S. l.], v. 28, p. 226–232, 1971. DOI: 10.7146/math.scand.a-11019. Disponível em: https://www.mscand.dk/article/view/11019. Acesso em: 3 may. 2024.