Agata Ciabattoni Lutz Straßburger Kazushige Terui Expanding the Realm of Systematic Proof Theory. 163-178 2009 CSL http://dx.doi.org/10.1007/978-3-642-04027-6_14 conf/csl/2009 db/conf/csl/csl2009.html#CiabattoniST09