Characterization Results for d-Horn Formulas Carlos Areces, Verónica Becher, Sebastián Ferro Abstract: Characterization Results for d­Horn Formulas (or: On formulas that are true on Dual Reduced Products) Carlos Areces, Ver\'onica Becher Sebasti\'an Ferro We provide two different model theoretic characterizations of a new fragment of first­order logic which we call d­Horn formulas. This fragment is dual to the well know Horn fragment and have the same complexity for provability. The method used in the characterization (syntactic translation functions between formulas which are mimicked by translation functions between models) might be applied to characterize other first­order restrictions. Keywords: Horn Formulas, d­Horn Formulas, Model Theoretic Characterizations.