it follows as a theorem from a set of axioms and inference rules. Especially by the work of Van Benthem (1986) and Moortgat (1988) this view, which we will name with Moortgat (1987a) Lambek Theorem Proving (LTP; Lambek, 1958), has become popular among a number of linguists. The descriptive power of LTP can be extended if unification (Shieber, 1986) is added. Several theories have been developed that combine categorial formalisms and unification based formalisms. Within Unification Categorial Grammar (UCG, Calder et al., 1988, Zeevat et al., 1986) unification "is the only operation over grammatical objects" (Calder et al. 1988,.
