KAUP, Wilhelm. Contractive projections on Jordan $C^*$-algebras and generalizations. Mathematica Scandinavica, Berkeley, CA, United States, v. 54, p. 95–100, 1984. DOI: 10.7146/math.scand.a-12043. Disponível em: https://journals.msp.org/mscand/article/view/1584. Acesso em: 25 jul. 2026.