Linguistics has always been a field with a great diversity of schools and sub-schools. This has naturally led to the question of whether different grammatical analyses of the same sentence are in fact equivalent or not. With the formalization of grammars as generative rule systems, beginning with the “Chomsky revolution” in the late nineteen fifties, it became possible to answer such questions in those fortunate instances in which the competing analyses were sufficiently formalized. An early example is the comparison of Context-Free Phrase Structure Grammar (CFPSG) and Bidirectional Categorial Grammar (BCG), which were shown to be weakly