中国科学院数学与系统科学研究院期刊网
AMS
The Order of Hypersubstitutions of Type(2, 2)
Thawhat CHANGPHAS, Klaus DENECKE
Acta Mathematica Sinica . 2007, (4): 659 -670 .  DOI: 10.1007/s10114-005-0778-z