Computations in choice groupoids

Defining achoice as a mapping of the subsets of a setX into their respective subsets, a one-to-one (and naturally) corresponding binary operation,sequential choice, is identified under which the power set ofX is closed as achoice groupoid. A complete logical diagram is given, exhibiting all the implications between conjunctions of the seven conditions: (1) idempotence, (2) consistency, (3) absorbence, and (4) homomorphism of a choice, and (5) commutativity, (6) associativity, and (7) path-independence of the corresponding sequential choice.     

Topological degree of a family of convex functions and localization of nash equilibrium points

We define the degree of a family of convex functionsf _x, wherex , and prove that, if this degree is different from zero, one has at least one Nash equilibrium point in . This is a criterion of localization of such equilibrium points.     

The core of discontinuous games

The traditional design of cooperative games implicitly assumes that preferences are continuous. However, if agents implement tie breaking procedures, preferences are effectively lexicographic and thus discontinuous. This rouses concern over whether classic core nonemptiness theorems apply in such settings. We show that balanced NTU games may have empty cores when agents have discontinuous preferences. Moreover, exchange economies may lack coalitionally rational trades when consumers implement tie breaking rules, even if these rules are themselves continuous and convex as are all first order preferences. Results are more positive when “utility” is transferable. We prove that balancedness is necessary and sufficient to ensure a nonempty core in lexicographic TU games.     

On Sets that Meet Every Hyperplane in n-Space in at Most n Points

A simple proof that no subset of the plane that meets everyline in precisely two points is an F-set in the plane is presented.It was claimed that this result can be generalized for setsthat meet every line in either one point or two points. No proofof this assertion is known, however. The main results in thispaper form a partial answer to the question of whether the claimis valid. In fact, it is shown that a set that meets every linein the plane in at least one but at most two points must bezero-dimensional, and that if it is -compact then it must bea nowhere dense G-set in the plane. Generalizations for similarsets in higher-dimensional Euclidean spaces are also presented.     

The ABC Conjecture Implies Vojta's Height Inequality for Curves

Following Elkies (Internat. Math. Res. Notices7 (1991) 99-109) and Bombieri (Roth's theorem and the abc-conjecture, preprint, ETH Zürich, 1994), we show that the ABC conjecture implies the one-dimensional case of Vojta's height inequality. The main geometric tool is the construction of a Belyǐ function. We take care to make explicit the effectivity of the result: we show that an effective version of the ABC conjecture would imply an effective version of Roth's theorem, as well as giving an (in principle) explicit bound on the height of rational points on an algebraic curve of genus at least two.     

Hitting time in a finite non-homogeneous Markov chain with applications

This paper deals with the computation of the hitting time for a non-homogeneous discrete time Markov chain (NHDTMC or NHMC). We first give the basic definitions of NHMC, then we analyse the hitting time and its survivor function. We also give the sufficient conditions for the existence of the mean hitting time. Finally, a numerical example and an application of this development in reliability evaluation are given in order to illustrate our results. © 1998 John Wiley & Sons, Ltd.     

Optimum parameters for the generalized ADI method

Summary. In the context of the generalized ADI method, we are concerned with the problem of finding in the set of rational functions r with numerator degree m and denominator degree n an element that minimizes where E,F are disjoint real intervals. By extending a recent analysis by Levin and Saff, we present an explicit formula for choosing the pair (m,n) for given m +n. Furthermore, we provide a characterization of and a Remes type algorithm for its determination. Extensive numerical computations furnish some comparison of with asymptotically optimal solutions based on Fejér-Walsh and Leja-Bagby points. Received September 6, 1996 / revised version received June 30, 1997     

Algebraic cycles and topology of real Enriques surfaces

For a real Enriques surface Y we prove that every homology class in H₁(Y (R), Z/2) can be represented by a real algebraic curve if and only if all connected components of Y(R) are orientable. Furthermore, we give a characterization of real Enriques surfaces which are Galois-Maximal and/or Z-Galois-Maximal and we determine the Brauer group of any real Enriques surface Y.     

A unified quantum <Emphasis Type="Italic">SO</Emphasis>(3) invariant for rational homology 3-spheres

Given a rational homology 3-sphere M with |H ₁(M,ℤ)|=b and a link L inside M, colored by odd numbers, we construct a unified invariant I _M,L belonging to a modification of the Habiro ring where b is inverted. Our unified invariant dominates the whole set of the SO(3) Witten–Reshetikhin–Turaev invariants of the pair (M,L). If b=1 and L=∅, I _M coincides with Habiro’s invariant of integral homology 3-spheres. For b>1, the unified invariant defined by the third author is determined by I _M . Important applications are the new Ohtsuki series (perturbative expansions of I _M ) dominating quantum SO(3) invariants at roots of unity whose order is not a power of a prime. These series are not known to be determined by the LMO invariant.     

The Clifford-Fourier Transform {mathcal {F}_o} and Monogenic Extensions

In the last decade several versions of the Fourier transform have been formulated in the framework of Clifford algebra. We present a (Clifford-Fourier) transform, constructed using the geometric properties of Clifford algebra. We show the corresponding results of operational calculus, and a connection between the Fourier transform and this new transform. We obtain a technique to construct monogenic extensions of a certain type of continuous functions, and versions of the Paley-Wiener theorems are formulated.