Agata Ciabattoni George Metcalfe Density Elimination and Rational Completeness for First-Order Logics. 132-146 2007 conf/lfcs/2007 LFCS http://dx.doi.org/10.1007/978-3-540-72734-7_10 db/conf/lfcs/lfcs2007.html#CiabattoniM07