INNAMI, Nobuhiro; KIM, Byung Hak. Gradient vector fields which characterize warped products. Mathematica Scandinavica, Berkeley, CA, United States, v. 88, n. 2, p. 182–192, 2001. DOI: 10.7146/math.scand.a-14322. Disponível em: https://journals.msp.org/mscand/article/view/883. Acesso em: 24 jul. 2026.