Hume, the Occult, and the Substance of the School

I have not been able to locate any critique of Hume on substance by a Schoolman, at least in English, dating from Hume's period or shortly thereafter. I have, therefore, constructed my own critique as an exercise in ??post facto history??. This is what a late eighteenth-century/early nineteenth-century Scholastic could, would, and should have said in response to Hume's attack on substance should they have been minded to do so. That no one did is somewhat mysterious. My critique is precisely in the language of the period, using solely the conceptual resources available to a Schoolman at that time. The arguments, however, are as sound now as they were then, and in this sense the paper performs a dual role??contributing to the defence of substance contra Hume, and filling, albeit two hundred?years or so too late, a gap in the historical record.     

Groups, measures, and the NIP

We discuss measures, invariant measures on definable groups, and genericity, often in an NIP (failure of the independence property) environment. We complete the proof of the third author's conjectures relating definably compact groups in saturated -minimal structures to compact Lie groups. We also prove some other structural results about such , for example the existence of a left invariant finitely additive probability measure on definable subsets of . We finally introduce the new notion of ``compact domination" (domination of a definable set by a compact space) and raise some new conjectures in the -minimal case.

     

On the Partially Ordered Semigroup Generated by the Class Operators I,R,H,S,P

Let I, H, S, P be the usual class operators on universal algebras. For a class K of universal algebras of the same type, let R({K}) be the class of all algebras isomorphic to a retract of a member of K and let R denote the corresponding class operator. In this paper the semigroup generated by class operators I, R, H, S, P and the corresponding partially ordered set are described. Also the standard semigroups of the above operators are determined for some varieties.     

The theorem of the alternative,the key-theorem,and the vector-maximum problem

Consequences of a general formulation of the theorem of the alternative are exploited.     

Wheels, wheeling, and the Kontsevich integral of the Unknot

We conjecture an exact formula for the Kontsevich integral of the unknot, and also conjecture a formula (also conjectured independently by Deligne [De]) for the relation between the two natural products on the space of uni-trivalent diagrams. The two formulas use the related notions of “Wheels” and “Wheeing”. We prove these formulas ‘on the level of Lie algebras’ using standard techniques from the theory of Vassiliev invariants and the theory of Lie algebras. In a brief epilogue we report on recent proofs of our full conjectures, by Kontsevich [Ko2] and by DBN, DPT, and T. Q. T. Le, [BLT]. This paper is available electronically     

Tilings,packings, coverings,and the approximation of functions

A packing (resp. covering) ? of a normed space X consisting of unit balls is called completely saturated (resp. completely reduced) if no finite set of its members can be replaced by a more numerous (resp. less numerous) set of unit balls of X without losing the packing property (resp. covering property) of ?. We show that a normed space X admits completely saturated packings with disjoint closed unit balls as well as completely reduced coverings with open unit balls, provided that there exists a tiling of X with unit balls. Completely reduced coverings by open balls are of interest in the context of an approximation theory for continuous real‐valued functions that rests on so‐called controllable coverings of compact metric spaces. The close relation between controllable coverings and completely reduced coverings allows an extension of the approximation theory to non‐compact spaces. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Quantum groups, the loop Grassmannian, and the Springer resolution

We establish equivalences of the following three triangulated categories:

Here, is the derived category of the principal block of finite-dimensional representations of the quantized enveloping algebra (at an odd root of unity) of a complex semisimple Lie algebra ; the category is defined in terms of coherent sheaves on the cotangent bundle on the (finite-dimensional) flag manifold for ( semisimple group with Lie algebra ), and the category is the derived category of perverse sheaves on the Grassmannian associated with the loop group , where is the Langlands dual group, smooth along the Schubert stratification.

The equivalence between and is an ``enhancement' of the known expression (due to Ginzburg and Kumar) for quantum group cohomology in terms of nilpotent variety. The equivalence between and can be viewed as a ``categorification' of the isomorphism between two completely different geometric realizations of the (fundamental polynomial representation of the) affine Hecke algebra that has played a key role in the proof of the Deligne-Langlands-Lusztig conjecture. One realization is in terms of locally constant functions on the flag manifold of a -adic reductive group, while the other is in terms of equivariant -theory of a complex (Steinberg) variety for the dual group.

The composite of the two equivalences above yields an equivalence between abelian categories of quantum group representations and perverse sheaves. A similar equivalence at an even root of unity can be deduced, following the Lusztig program, from earlier deep results of Kazhdan-Lusztig and Kashiwara-Tanisaki. Our approach is independent of these results and is totally different (it does not rely on the representation theory of Kac-Moody algebras). It also gives way to proving Humphreys' conjectures on tilting -modules, as will be explained in a separate paper.     

Kant, Spinoza, and the Metaphysics of the Ontological Proof

This paper provides an interpretation and evaluation of Spinoza’s highly original version of the ontological proof in terms of the concept of substance instead of the concept of perfection in the first book of his Ethics. Taking the lead from Kant’s critique of ontological arguments in the Critique of Pure Reason, the paper explores the underlying ontological and epistemological presuppositions of Spinoza’s proof. The main topics of consideration are the nature of Spinoza’s definitions, the way he conceives of the relation between a substance and its essence, and his conception of existence. Once clarity is shed upon these fundamental issues, it becomes possible to address the proof in its own terms. It is then easy to see that Kant’s objections miss their target and that the same is true of those advanced by another of the ontological argument’s most famous critics, Bertrand Russell. Finally, several interpretations of Spinoza’s proof are proposed and critically evaluated; on all of them, the argument turns out to be either invalid or question-begging.     

Concerning the Collins, Reed, Roscoe, Rudin Metrisation Theorem

New criteria, in terms of the Collins-Roscoe structuring mechanism,are given for a space to be semi-stratifiable. Known characterisationsof metrisable, developable and stratifiable spaces are deduced.     

Collusion,quarrel, and the Banzhaf value

We provide new, concise characterizations of the Banzhaf value on a fixed player set employing just the standard dummy player property and one of the collusion properties suggested by Haller (Int J Game Theory 23:261–281, 1994) and Malawski (Int J Game Theory 31:47–67, 2002). Within these characterizations, any of the collusion properties can be replaced by additivity and the quarrel property due to the latter author.     

Maximax, leximax, and the demanding criterion

Following the characterizations provided by Barberà and Jackson [Barberà, S., Jackson, M.O., 1988. Journal of Economic Theory 46, 34–44] for the maximin, the leximin, and the protective criterion, we examine the consequences of replacing convexity in their list of axioms by concavity, which means considering risk-loving instead of risk-averse agents. This yields characterizations of the maximax, the leximax and a new criterion which we term demanding criterion. We concentrate on the latter and demonstrate the independence of the axioms used for its characterization.