Atlas of the world's languages
Routledge: 1994,
 Buku Referensi
Atlas of the world languages
Routledge, 2007
 Buku Referensi
Atlas of the world's languages
general editors, Christopher Moseley and R.E. Asher; section editors Mary Tait ... [and others]
Routledge, New York Routledge Reference 1994
 Buku Referensi
Atlas of the world's languages
general editors, Christopher Moseley, R.E. Asher
Routledge, 1994
 Buku Referensi
Eilenberg, Samuel
Automata, languages, and machines; Volume B
Academic Press, 1976
 Buku Teks SO