ROBINSON, Derek W. Commutators and generators II. MATHEMATICA SCANDINAVICA, [S. l.], v. 64, p. 87–108, 1989. DOI: 10.7146/math.scand.a-12249. Disponível em: https://tidsskrift.dk/math/article/view/12249. Acesso em: 14 aug. 2026.