中国科学院数学与系统科学研究院期刊网
The Classification of All Quantifier-Eliminable Directed or Undirected Trees with a Root
Ying Ying FU, Fu Xing SHEN
Acta Mathematica Sinica, Chinese Series . 2015, (4): 691 -704 .  DOI: 10.12386/A2015sxxb0071