CHUNG, K. L. On the Exponential Formulas of Semi-Group Theory. MATHEMATICA SCANDINAVICA, [S. l.], v. 10, p. 153–162, 1962. DOI: 10.7146/math.scand.a-10522. Disponível em: https://www.mscand.dk/article/view/10522. Acesso em: 14 apr. 2025.