This paper shows how to use the UnfoldFold transformation to transform Projective Bilexical Dependency Grammars (PBDGs) into ambiguity-preserving weakly equivalent Context-Free Grammars (CFGs). These CFGs can be parsed in O(n3 ) time using a CKY algorithm with appropriate indexing, rather than the O(n5 ) time required by a naive encoding. Informally, using the CKY algorithm with such a CFG mimics the steps of the Eisner-Satta O(n3 ) PBDG parsing algorithm. This transformation makes all of the techniques developed for CFGs available to PBDGs. .
