TY  - DATA
AU  - Ginsburg, Seymour
AU  - Greibach, Sheila,Hopcroft, John E.,
TI  - Studies in abstract families of languages 
T2  - Memoirs of the American Mathematical Society, 
SN  - 9781470400361 (online)
PY  - 1969///
CY  - Providence, R.I.
PB  - American Mathematical Society
UR  - http://www.ams.org/memo/0087
ER  -