中国科学院数学与系统科学研究院期刊网
On Happel’s Question and Snashall-Solberg’s Conjecture
Yun Ge XU, Chao ZHANG
Acta Mathematica Sinica, Chinese Series . 2012, (6): 1067 -1084 .  DOI: 10.12386/A2012sxxb0103