Arnoldo José Müller Molina Kouichi Hirata Takeshi Shinohara A Tree Distance Function Based on Multi-sets. 87-98 2008 PAKDD Workshops http://dx.doi.org/10.1007/978-3-642-00399-8_8 conf/pakdd/2008w db/conf/pakdd/pakdd2008w.html#MolinaHS08