CHUNG, Kai Lai. On the Exponential Formulas of Semi-Group Theory. Mathematica Scandinavica, Berkeley, CA, United States, v. 10, p. 153–162, 1962. DOI: 10.7146/math.scand.a-10522. Disponível em: https://journals.msp.org/mscand/article/view/2666. Acesso em: 25 jul. 2026.