Petr Savický Roberto Cignoli Francesc Esteva Lluis Godo Carles Noguera On Product Logic with Truth-constants. 205-225 2006 16 J. Log. Comput. 2 http://dx.doi.org/10.1093/logcom/exi075 db/journals/logcom/logcom16.html#SavickyCEGN06