KOMOROWSKI, Tomasz; WOSKO, Jacek. A remark on the retracting of a ball onto a sphere in an infinite dimensional Hilbert space. Mathematica Scandinavica, Berkeley, CA, United States, v. 67, p. 223–226, 1990. DOI: 10.7146/math.scand.a-12334. Disponível em: https://journals.msp.org/mscand/article/view/1342. Acesso em: 25 jul. 2026.