Yannick Parmentier Joseph Le Roux Benoît Crabbé XMG - An Expressive Formalism for Describing Tree-Based Grammars. 2006 conf/eacl/2006 EACL http://acl.ldc.upenn.edu/E/E06/E06-2005.pdf db/conf/eacl/eacl2006.html#ParmentierRC06