ASLAKSEN, Helmer. $\mathrm{SO}(2)$ invariants of a set of $2 \times 2$ matrices. MATHEMATICA SCANDINAVICA, [S. l.], v. 65, p. 59–66, 1989. DOI: 10.7146/math.scand.a-12265. Disponível em: https://tidsskrift.dk/math/article/view/12265. Acesso em: 14 aug. 2026.