ÉSIK, Z.; KUICH, W. Formal Tree Series. BRICS Report Series, [S. l.], v. 9, n. 21, 2002. DOI: 10.7146/brics.v9i21.21737. Disponível em: https://tidsskrift.dk/brics/article/view/21737. Acesso em: 23 apr. 2024.