Pietro Baroni Federico Cerutti Massimiliano Giacomin Giovanni Guida Encompassing Attacks to Attacks in Abstract Argumentation Frameworks. 83-94 2009 ECSQARU http://dx.doi.org/10.1007/978-3-642-02906-6_9 conf/ecsqaru/2009 db/conf/ecsqaru/ecsqaru2009.html#BaroniCGG09