ASLAKSEN, Helmer. $\mathrm{SO}(2)$ invariants of a set of $2 \times 2$ matrices. Mathematica Scandinavica, Berkeley, CA, United States, v. 65, p. 59–66, 1989. DOI: 10.7146/math.scand.a-12265. Disponível em: https://journals.msp.org/mscand/article/view/1385. Acesso em: 25 jul. 2026.