ABRAHAMSEN, Trond A. Strict U-Ideals and U-Summands in Banach Spaces. Mathematica Scandinavica, Berkeley, CA, United States, v. 114, n. 2, p. 216–225, 2014. DOI: 10.7146/math.scand.a-17108. Disponível em: https://journals.msp.org/mscand/article/view/424. Acesso em: 24 jul. 2026.