OKAYASU, Rui. $C^*$-algebras associated with the fundamental groups of graphs of groups. Mathematica Scandinavica, Berkeley, CA, United States, v. 97, n. 1, p. 49–72, 2005. DOI: 10.7146/math.scand.a-14963. Disponível em: https://journals.msp.org/mscand/article/view/734. Acesso em: 25 jul. 2026.