SALOMAA, A. On essential variables of functions, especially in the algebra of logic. Annales Fennici Mathematici, [S. l.], n. 339, 1964. DOI: 10.5186/aasfm.1964.339. Disponível em: https://afm.journal.fi/article/view/134041. Acesso em: 26 nov. 2024.