José L. Balcázar Albert Bifet Antoni Lozano Subtree Testing and Closed Tree Mining Through Natural Representations. 499-503 2007 conf/dexaw/2007 DEXA Workshops http://doi.ieeecomputersociety.org/10.1109/DEXA.2007.130 db/conf/dexaw/dexaw2007.html#BalcazarBL07