Abstract

Joel M. Cohen , pp. 475- 484) claims that Lambek’s categorial grammars are equivalent in a certain natural sense to those of Bar-Hillel, Gaifman, and Shamir. Unfortunately, it turns out that Cohen’s proof is based on a false lemma. Thus the equivalence of both kinds of grammars is still an open problem although there is much evidence in its favor. This paper yields a counterexample to Cohen’s lemma