Fabio Aiolli Giovanni Da San Martino Alessandro Sperduti Extending Tree Kernels with Topological Information. 142-149 2011 ICANN (1) http://dx.doi.org/10.1007/978-3-642-21735-7_18 conf/icann/2011-1 db/conf/icann/icann2011-1.html#AiolliMS11