LEPISTÖ, T. An extension for the concept of finite index of a context-free grammar. Annales Fennici Mathematici, [S. l.], n. 518, 1972. DOI: 10.5186/aasfm.1972.518. Disponível em: https://afm.journal.fi/article/view/134174. Acesso em: 26 nov. 2024.