Dominique Duval Rachid Echahed Frédéric Prost A Heterogeneous Pushout Approach to Term-Graph Transformation. 194-208 2009 RTA http://dx.doi.org/10.1007/978-3-642-02348-4_14 conf/rta/2009 db/conf/rta/rta2009.html#DuvalEP09