KROM, M. R. The Decision Problem for Segregated Formulas in First-Order Logic. Mathematica Scandinavica, Berkeley, CA, United States, v. 21, p. 233–240, 1967. DOI: 10.7146/math.scand.a-10862. Disponível em: https://journals.msp.org/mscand/article/view/2463. Acesso em: 25 jul. 2026.