Ultrafilters and multidimensional Ramsey Theorems

Utilizing ultrafilters on the setN of natural numbers which have certain special properties, we prove some simultaneous generalizations of Ramsey's Theorem and several single dimension Ramsey-type theorems. (For instance, as a very special case, we obtain a simultaneous generalization of Ramsey's Theorem and van der Waerden's Theorem.) Examples are given to show directions in which these results cannot be extended.     

Social choice theory without Pareto: The pivotal voter approach

This paper extends the pivotal voter approach pioneered by Barberá [Barberá, S., 1980. Pivotal voters: A new proof of Arrow’s Theorem. Economics Letters 6, 13–6; Barberá, S., 1983. Strategy-proofness and pivotal voters: A direct proof of the Gibbard-Satterthwaite Theorem. International Economic Review 24, 413–7] to all social welfare functions satisfying independence of irrelevant alternatives. Arrow’s Theorem, Wilson’s Theorem, and the Muller–Satterthwaite Theorem are all immediate corollaries of the main result. It is further shown that a vanishingly small fraction of pairs of alternatives can be affected in the group preference ordering by multiple individuals, which generalizes each of the above theorems.     

A Result in Dual Ramsey Theory

We present a result which is obtained by combining a result of Carlson with the Finitary Dual Ramsey Theorem of Graham–Rothschild.     

Homogeneous sets from several ultrafilters

We consider Ramsey-style partition theorems in which homogeneity is asserted not for subsets of a single infinite homogeneous set but for subsets whose elements are chosen, in a specified pattern, from several sets in prescribed ultrafilters. We completely characterize the sequences of ultrafilters satisfying such partition theorems. (Non-isomorphic selective ultrafilters always work, but, depending on the specified pattern, weaker hypotheses on the ultrafilters may suffice.) We also obtain similar results for analytic partitions of the infinite sets of natural numbers. Finally, we show that the two P-points obtained by applying the maximum and minimum functions to a union ultrafilter are never nearly coherent.     

Weak subdifferential for set-valued mappings and its applications

In this paper, the existence theorems of two kinds of weak subgradients for set-valued mappings, which are the generalizations of Theorem 7 in [G.Y. Chen, J. Jahn, Optimality conditions for set-valued optimization problems, Math. Methods Oper. Res. 48 (2) (1998) 187–200] and Theorem 4.1 in [J.W. Peng, H.W.J. Lee, W.D. Rong, X.M. Yang, Hahn–Banach theorems and subgradients of set-valued maps, Math. Methods Oper. Res. 61 (2005) 281–297], respectively, are proved by virtue of a Hahn–Banach extension theorem. Moreover, some properties of the weak subdifferential for set-valued mappings are obtained by using a so-called Sandwich theorem. Finally, necessary and sufficient optimality conditions are discussed for set-valued optimization problems, whose constraint sets are determined by a fixed set and a set-valued mapping, respectively.     

\mathcal{D}†-affinité de l'espace projectif

We proove an analogue of the Beilinson–Bernstein Theorem, in the case of the projective space, for the ring of arithmetical differential operators introduced by P. Berthelot.     

Four functionals fixed point theorem

The Four Functionals Fixed Point Theorem is a generalization of the original, as well as the functional generalizations, of the Leggett–Williams Fixed Point Theorem. In the Four Functionals Fixed Point Theorem, neither the upper nor the lower boundary of the underlying set is required to map below or above the boundary in the functional sense. As an application, the existence of a positive solution to a second-order right focal boundary value problem is considered by applying both standard and nonstandard choices of functionals. An extension to multivalued maps is provided for completeness.     

Extremal problems,partition theorems,symmetric hypergraphs

We compare extremal theorems such as Turán’s theorem with their corresponding partition theorems such as Ramsey’s theorem. We derive a general inequality involving chromatic number and independence number of symmetric hypergraphs. We give applications to Ramsey numbers and to van der Waerden numbers.     

VIP systems in partial semigroups

A VIP system is a polynomial-type generalization of the notion of an IP system, i.e., a set of finite sums. We extend the notion of VIP system to commutative partial semigroups and obtain an analogue of Furstenberg's central sets theorem for these systems which extends the polynomial Hales–Jewett Theorem of Bergelson and Leibman. Several Ramsey theoretic consequences, including the central sets theorem itself, are then derived from these results.     

The Hahn–Banach Theorem for Partially Ordered Totally Convex, Positively Convex and Superconvex Modules

The Hahn–Banach Theorem for partially ordered totally convex modules [3] and a necessary and sufficient condition for the existence of an extension of a morphism from a submodule C ₀ of a partially ordered totally convex module C (with the ordered unit ball of the reals as codomain) to C, are proved. Moreover, the categories of partially ordered positively convex and superconvex modules are introduced and for both categories the Hahn–Banach Theorem is proved.     

Bootstraps of sums of independent but not identically distributed stochastic processes

A central limit theorem is developed for sums of independent but not identically distributed stochastic processes multiplied by independent real random variables with mean zero. Weak convergence of the Hoffmann–Jørgensen–Dudley type, as described in van der Vaart and Wellner (Weak Convergence and Empirical Processes, Springer, New York, 1996), is utilized. These results allow Monte Carlo estimation of limiting probability measures obtained from application of Pollard's (Empirical Processes: Theory and Applications, IMS, Hayward, CA, 1990) functional central limit theorem for empirical processes. An application of this theory to the two-parameter Cox score process with staggered entry data is given for illustration. For this process, the proposed multiplier bootstrap appears to be the first successful method for estimating the associated limiting distribution. The results of this paper compliment previous bootstrap and multiplier central limit theorems for independent and identically distributed empirical processes.     

Algebras, hyperalgebras, nonassociative bialgebras and loops

Sabinin algebras are a broad generalization of Lie algebras that include Lie, Malcev and Bol algebras as very particular examples. We present a construction of a universal enveloping algebra for Sabinin algebras, and the corresponding Poincaré-Birkhoff-Witt Theorem. A nonassociative counterpart of Hopf algebras is also introduced and a version of the Milnor-Moore Theorem is proved. Loop algebras and universal enveloping algebras of Sabinin algebras are natural examples of these nonassociative Hopf algebras. Identities of loops move to identities of nonassociative Hopf algebras by a linearizing process. In this way, nonassociative algebras and Hopf algebras interlace smoothly.     

Noncommutataive Descent and Non-Abelian Cohomology

We study the descent problem of modules over general extensions of noncommutative rings and give different interpretations of descent data. We consider in particular the case of Hopf–Galois extensions. When descent data exist, we classify them by non-Abelian cohomology sets and deduce a noncommutative version of Hilbert's Theorem 90.     

Marcinkiewicz–Zygmund inequalities

We study a generalization of the classical Marcinkiewicz–Zygmund inequalities. We relate this problem to the sampling sequences in the Paley–Wiener space and by using this analogy we give sharp necessary and sufficient computable conditions for a family of points to satisfy the Marcinkiewicz–Zygmund inequalities.     

The canonical Ramsey theorem and computability theory

Using the tools of computability theory and reverse mathematics, we study the complexity of two partition theorems, the Canonical Ramsey Theorem of Erdös and Rado, and the Regressive Function Theorem of Kanamori and McAloon. Our main aim is to analyze the complexity of the solutions to computable instances of these problems in terms of the Turing degrees and the arithmetical hierarchy. We succeed in giving a sharp characterization for the Canonical Ramsey Theorem for exponent 2 and for the Regressive Function Theorem for all exponents. These results rely heavily on a new, purely inductive, proof of the Canonical Ramsey Theorem. This study also unearths some interesting relationships between these two partition theorems, Ramsey's Theorem, and König's Lemma.

     

Truth‐table Schnorr randomness and truth‐table reducible randomness

Schnorr randomness and computable randomness are natural concepts of random sequences. However van Lambalgen’s Theorem fails for both randomnesses. In this paper we define truth‐table Schnorr randomness (defined in 6 too only by martingales) and truth‐table reducible randomness, for which we prove that van Lambalgen's Theorem holds. We also show that the classes of truth‐table Schnorr random reals relative to a high set contain reals Turing equivalent to the high set. It follows that each high Schnorr random real is half of a real for which van Lambalgen's Theorem fails. Moreover we establish the coincidence between triviality and lowness notions for truth‐table Schnorr randomness. © 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

The limiting case of Haglund's (q,t)-Schröder theorem and an involution formula

As a generalization of Haglund's statistic on Dyck paths [Conjectured statistics for the q,t-Catalan numbers, Adv. Math. 175 (2) (2003) 319–334; A positivity result in the theory of Macdonald polynomials, Proc. Nat. Acad. Sci. 98 (2001) 4313–4316], Egge et al. introduced the (q,t)-Schröder polynomial S_n,d(q,t), which evaluates to the Schröder number when q=t=1 [A Schröder generalization of Haglund's statistic on Catalan paths, Electron. J. Combin. 10 (2003) 21pp (Research Paper 16, electronic)]. In their paper, S_n,d(q,t) was conjectured to be equal to the coefficient of a hook shape on the Schur function expansion of the symmetric function e_n, which Haiman [Vanishing theorems and character formulas for the Hilbert scheme of points in the plane, Invent. Math. 149 (2002) 371–407] has shown to have a representation-theoretic interpretation. This conjecture was recently proved by Haglund [A proof of the q,t-Schröder conjecture, Internat. Math. Res. Not. (11) (2004) 525–560]. However, because that proof makes heavy use of symmetric function identities and plethystic machinery, the combinatorics behind it is not understood. Therefore, it is worthwhile to study it combinatorially. This paper investigates the limiting case of the (q,t)-Schröder Theorem and obtains interesting results by looking at some special cases.     

Modeling Multiparticle Coherences in Solid-State Nuclear Spin Systems Using Infinite-Range Interaction

Using the exactly solvable model known in statistical physics as the infinite-range interaction model (the van der Waals model), we obtain expressions for the hierarchy of multispin multiquantum time correlation functions for a solid-state paramagnetic nuclear spin system with magnetic dipole–dipole interaction between nuclei. These functions are observed experimentally using contemporary multiquantum NMR spectroscopy methods. We write the complete set of orthogonal multispin operators explicitly and find the time dependence for amplitudes of multiparticle time correlation functions. The proposed model describes the behavior of multiparticle correlation functions well, at least for not very large numbers n of expansion harmonics. The theoretical results agree well with the experimental data obtained for hexamethylbenzol.     

Transformée de Mellin des intégrales-fibres associées aux singularités isolées d'intersection complète quasihomogènes. (Mellin Transform of Fibre Integrals Associated to Isolated Complete Intersection Singularities)

The Mellin transform of the fibre integral is calculated for certain quasihomogeneous isolated complete intersection singularities (above all, unimodal singularities of the list by Giusti and Wall). We show the symmetry property of the Gauss–Manin spectra (Theorem 3.1) and shed light on the lattice structure of the poles of the Mellin transform that are expressed by means of some topological data of the singularities (Theorem 4.3, Theorem 5.2). As an application of these results, we express the Hodge number of the fibre in terms of the Gauss–Manin spectra.