HIRANO, Yasuyuki. On $\pi$-regular rings with no infinite trivial subring. Mathematica Scandinavica, Berkeley, CA, United States, v. 63, p. 212–214, 1988. DOI: 10.7146/math.scand.a-12234. Disponível em: https://journals.msp.org/mscand/article/view/1432. Acesso em: 25 jul. 2026.