Readers of these lists may be interested to hear that the following paper has appeared: C. Führmann and D. Pym. On categorical models of classical logic and the geometry of interaction. Mathematical Structures in Computer Science 17(5), 2007, 957-1027. Abstract. It is well known that weakening and contraction cause naive categorical models of the classical sequent calculus to collapse to Boolean lattices. In previous work, summarised briefly herein, we have provided a class of models called /classical categories/ that is sound and complete and avoids this collapse by interpreting cut reduction by a poset enrichment. Examples of classical categories include boolean lattices and the category of sets and relations, where both conjunction and disjunction are modelled by the set-theoretic product. In this article, which is self-contained, we present an improved axiomatisation of classical categories, together with a deep exploration of their structural theory. Observing that the collapse already happens in the absence of negation, we start with negation-free models called /Dummett categories/. Examples of these include, besides the classical categories mentioned above, the category of sets and relations, where both conjunction and disjunction are modelled by the disjoint union. We prove that Dummett categories are MIX, and that the partial order can be derived from hom-semilattices, which have a straightforward proof-theoretic definition. Moreover, we show that the Geometry-of-Interaction construction can be extended from multiplicative linear logic to classical logic by applying it to obtain a classical category from a Dummett category. Along the way, we gain detailed insights into the changes that proofs undergo during cut elimination in the presence of weakening and contraction. -- Prof. David J. Pym t: +44 (0) 117 312 8012 Principal Scientist f: +44 (0) 117 312 9250 HP Labs e: david.pym@hp.com Bristol, UK w: http://www.hpl.hp.com/personal/davpym/ Professor of Logic & Computation, University of Bath, UK