ANDERSEN, A. F. A Condition for $C$-Summability of Negative Order. Mathematica Scandinavica, Berkeley, CA, United States, v. 7, p. 337–346, 1959. DOI: 10.7146/math.scand.a-10579. Disponível em: https://journals.msp.org/mscand/article/view/2767. Acesso em: 8 sep. 2026.