Janusz Czelakowski Don Pigozzi Fregean logics with the multiterm deduction theorem and their algebraization. 171-212 2004 78 Studia Logica 1-2 http://www.springerlink.com/index/10.1007/s11225-005-1212-3 db/journals/sLogica/sLogica78.html#CzelakowskiP04