HIRANO, Yasuyuki. On $\pi$-regular rings with no infinite trivial subring. MATHEMATICA SCANDINAVICA, [S. l.], v. 63, p. 212–214, 1988. DOI: 10.7146/math.scand.a-12234. Disponível em: https://tidsskrift.dk/math/article/view/12234. Acesso em: 14 aug. 2026.