Rosalie Iemhoff George Metcalfe Hypersequent Systems for the Admissible Rules of Modal and Intermediate Logics. 230-245 2009 LFCS http://dx.doi.org/10.1007/978-3-540-92687-0_16 conf/lfcs/2009 db/conf/lfcs/lfcs2009.html#IemhoffM09