ZHANG, S. Homotopy of projections and factorization in the unitary group of certain $C^*$-algebras. MATHEMATICA SCANDINAVICA, [S. l.], v. 73, p. 281–306, 1993. DOI: 10.7146/math.scand.a-12472. Disponível em: https://www.mscand.dk/article/view/12472. Acesso em: 4 may. 2024.