HENNO, J. On idempotents and Green relations in the algebras of many-placed functions. Annales Fennici Mathematici, [S. l.], v. 2, n. 1, p. 169–178, 1976. DOI: 10.5186/aasfm.1977.0309. Disponível em: https://afm.journal.fi/article/view/134289. Acesso em: 25 nov. 2024.