TY  - DATA
AU  - Sommerhauser, Yorck
AU  - Zhu, Yongchang.
TI  - Hopf algebras and congruence subgroups 
T2  - Memoirs of the American Mathematical Society, 
SN  - 9780821891087 (online)
PY  - 2011///
CY  - Providence, R.I.
PB  - American Mathematical Society
UR  - http://www.ams.org/memo/1028
ER  -