1. Chi, Y., Yang, Y., Muntz, R.R.: HybridTreeMiner: an efficient algorithm for mining frequent rooted trees and free trees using canonical forms. In: Proceedings of the 16th International Conference on Scientific and Statistical Database Management, pp. 11–20. IEEE, Santorini (2004)
2. Chi, Y., Yang, Y., Muntz, R.R.: Indexing and mining free trees. In: Third IEEE International Conference on Data Mining, ICDM 2003, pp. 509–512. IEEE (2003)
3. Zhao, P., Yu, J.: Fast frequent free tree mining in graph databases. World Wide Web 11(1), 71–92 (2008)
4. Rückert, U., Kramer, S.: Frequent free tree discovery in graph data. In: Proceedings of the 2004 ACM Symposium on Applied Computing, pp. 564–570. ACM (2004)
5. Hein, J., Jiang, T., Wang, L., Zhang, K.: On the complexity of comparing evolutionary trees. Discrete Appl. Math. 71(1), 153–169 (1996)