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.