@InCollection{ BeckertHaehnleManyaLD99, author = {Bernhard Beckert and Reiner H\"ahnle and Felip Manya}, title = {The SAT Problem of Signed CNF Formulas}, booktitle = {Labelled Deduction}, editor = {M. D'Agostino and D. Basin and D. Gabbay and S. Matthews and L. Vigano}, pages = {59--80}, publisher = {Kluwer, Dordrecht}, year = {2000} }