Polarized Unification Grammars 
 
 This paper proposes a generic mathematical formalism for the combination of various structures : strings , trees , dags , graphs , and products of them. The polarization of the objects of the elementary structures controls the saturation of the final structure . This formalism is both elementary and powerful enough to strongly simulate many grammar formalisms , such as rewriting systems , dependency grammars , TAG , HPSG and LFG .  