Witt equivalence of algebraic function fields over real closed fields

We examine the conditions for two algebraic function fields over real closed fields to be Witt equivalent. We show that there are only two Witt classes of algebraic function fields with a fixed real closed field of constants: real and non-real ones. The first of them splits further into subclasses corresponding to the tame equivalence. This condition has a natural interpretation in terms of both: orderings (the associated Harrison isomorphism maps 1-pt fans onto 1-pt fans), and geometry and topology of associated real curves (the bijection of points is a homeomorphism and these two curves have the same number of semi-algebraically connected components). Finally, we derive some immediate consequences of those theorems. In particular we describe all the Witt classes of algebraic function fields of genus 0 and 1 over the fixed real closed field. Received: 16 February 2000; in final form: 7 December 2000 / Published online: 18 January 2002     

Bredon-style homology, cohomology and Riemann-Roch for algebraic stacks

One of the main obstacles for proving Riemann-Roch for algebraic stacks is the lack of cohomology and homology theories that are closer to the K-theory and G-theory of algebraic stacks than the traditional cohomology and homology theories for algebraic stacks. In this paper we study in detail a family of cohomology and homology theories which we call Bredon-style theories that are of this type and in the spirit of the classical Bredon cohomology and homology theories defined for the actions of compact topological groups on topological spaces. We establish Riemann-Roch theorems in this setting: it is shown elsewhere that such Riemann-Roch theorems provide a powerful tool for deriving formulae involving virtual fundamental classes associated to dg-stacks, for example, moduli stacks of stable curves provided with a virtual structure sheaf associated to a perfect obstruction theory. We conclude the present paper with a brief application of this nature.     

Incidence Theorems for Pseudoflats

We prove Pach-Sharir type incidence theorems for a class of curves in Rⁿ and surfaces in R³, which we call pseudoflats}. In particular, our results apply to a wide class of generic irreducible real algebraic sets of bounded degree.     

An algebraic treatment of quantifier-free systems of arithmetic

By algebraic means, we give an equational axiomatization of the equational fragments of various systems of arithmetic. We also introduce a faithful semantics according to which, for every reasonable system for arithmetic, there is a model where exactly the theorems of are true. Received March 20, 1995     

The Nother and Riemann-Roch type theorems for piecewise algebraic curve

A piecewise algebraic curve is a curve determined by the zero set of a bivariate spline function. In this paper, the Nother type theorems for Cμpiecewise algebraic curves are obtained. The theory of the linear series of sets of places on the piecewise algebraic curve is also established. In this theory, singular cycles are put into the linear series, and a complete series of the piecewise algebraic curves consists of all effective ordinary cycles in an equivalence class and all effective singular cycles which are equivalent specifically to any effective ordinary cycle in the equivalence class. This theory is a generalization of that of linear series of the algebraic curve. With this theory and the fundamental theory of multivariate splines on smoothing cofactors and global conformality conditions, and the results on the general expression of multivariate splines, we get a formula on the index, the order and the dimension of a complete series of the irreducible Cμpiecewise algebraic curves and the degree, the genus and the smoothness of the curves, hence the Riemann-Roch type theorem of the Cμpiecewise algebraic curve is established.     

The Nöther and Riemann-Roch type theorems for piecewise algebraic curve

A piecewise algebraic curve is a curve determined by the zero set of a bivariate spline function. In this paper, the Nöther type theorems for C ^µ piecewise algebraic curves are obtained. The theory of the linear series of sets of places on the piecewise algebraic curve is also established. In this theory, singular cycles are put into the linear series, and a complete series of the piecewise algebraic curves consists of all effective ordinary cycles in an equivalence class and all effective singular cycles which are equivalent specifically to any effective ordinary cycle in the equivalence class. This theory is a generalization of that of linear series of the algebraic curve. With this theory and the fundamental theory of multivariate splines on smoothing cofactors and global conformality conditions, and the results on the general expression of multivariate splines, we get a formula on the index, the order and the dimension of a complete series of the irreducible C ^µ piecewise algebraic curves and the degree, the genus and the smoothness of the curves, hence the Riemann-Roch type theorem of the C ^µ piecewise algebraic curve is established.     

Mechanical theorem proving in the surfaces using the characteristic set method and Wronskian determinant

In this paper, we generalize the method of mechanical theorem proving in curves to prove theorems about surfaces in differential geometry with a mechanical procedure. We improve the classical result on Wronskian determinant, which can be used to decide whether the elements in a partial differential field are linearly dependent over its constant field. Based on Wronskian determinant, we can describe the geometry statements in the surfaces by an algebraic language and then prove them by the characteristic set method.     

Real separated algebraic curves, quadrature domains, Ahlfors type functions and operator theory

The aim of this paper is to inter-relate several algebraic and analytic objects, such as real-type algebraic curves, quadrature domains, functions on them and rational matrix functions with special properties, and some objects from operator theory, such as vector Toeplitz operators and subnormal operators. Our tools come from operator theory, but some of our results have purely algebraic formulation. We make use of Xia's theory of subnormal operators and of the previous results by the author in this direction. We also correct (in Section 5) some inaccuracies in the works of [D.V. Yakubovich, Subnormal operators of finite type I. Xia's model and real algebraic curves in C², Rev. Mat. Iberoamericana 14 (1998) 95-115; D.V. Yakubovich, Subnormal operators of finite type II. Structure theorems, Rev. Mat. Iberoamericana 14 (1998) 623-681] by the author.     

Measures of Simultaneous Approximation for Quasi-Periods of Abelian Varieties

We examine various extensions of a series of theorems proved by Chudnovsky in the 1980s on the algebraic independence (transcendence degree 2) of certain quantities involving integrals of the first and second kind on elliptic curves; these extensions include generalizations to abelian varieties of arbitrary dimensions, quantitative refinements in terms of measures of simultaneous approximation, as well as some attempt at unifying the aforementioned theorems. In the process we develop tools that might prove useful in other contexts, revolving around explicit “algebraic” theta functions on the one hand, and Eisenstein's theorem and G-functions on the other hand.     

Uniqueness theorems for algebraic functions that take the number of algebraic elements into account

We obtain uniqueness theorems for algebraic functions that take into account not onlyA-points but also the number of covering elements located above them.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 47, No. 11, pp. 1498–1505, November, 1995.     

Conditions imposed by tacnodes and cusps

The study of linear systems of algebraic plane curves with fixed imposed singularities is a classical subject which has recently experienced important progress. The Horace method introduced by A. Hirschowitz has been successfully exploited to prove many -vanishing theorems, even in higher dimension. Other specialization techniques, which include degenerations of the plane, are due to Z. Ran and C. Ciliberto and R. Miranda. G. M. Greuel, C. Lossen and E. Shustin use a local specialization procedure together with the Horace method to give the first asymptotically proper general existence criterion for singular curves of low degree. In this paper we develop a specialization method which allows us to compute the dimension of several linear systems as well as to substantially improve the bounds given by Greuel, Lossen and Shustin for curves with tacnodes and cusps.

     

Arithmetic properties of values of analytic functions connected by algebraic equations over fields of rational functions

In this paper theorems are proved about the arithmetic character of the values at algebraic points of a collection of G-functions which constitute a solution of a system of linear differential equations with coefficients from C(z) connected by algebraic equations over C(z). In addition, the theorems on E-functions proved by A. B. Shidlovskii in 1962 are supplemented.Translated from Matematicheskie Zametki, Vol. 14, No. 1, pp. 83–94, July, 1973.In conclusion, I express thanks to A. B. Shidlovskii for attention to and help with this work.     

Algebraic Logic for Rational Pavelka Predicate Calculus

In this paper we define the polyadic Pavelka algebras as algebraic structures for Rational Pavelka predicate calculus (RPL∀). We prove two representation theorems which are the algebraic counterpart of the completness theorem for RPL∀.     

Almost fifth powers in arithmetic progression

We prove that the product of k consecutive terms of a primitive arithmetic progression is never a perfect fifth power when 3?k?54. We also provide a more precise statement, concerning the case where the product is an “almost” fifth power. Our theorems yield considerable improvements and extensions, in the fifth power case, of recent results due to Gy?ry, Hajdu and Pintér. While the earlier results have been proved by classical (mainly algebraic number theoretical) methods, our proofs are based upon a new tool: we apply genus 2 curves and the Chabauty method (both the classical and the elliptic verison).     

Commutativity theorems in rings with involution

In this paper, we investigate commutativity of ring R with involution ? which admits a derivation satisfying certain algebraic identities. Some well-known results characterizing commutativity of prime rings have been generalized. Finally, we provide examples to show that various restrictions imposed in the hypotheses of our theorems are not superfluous.     

Algebraic theory of differential inequalities

We obtain differential-algebraic analogues of some basic theorems of real algebra and semialgebraic geometry. Proofs are based on: a differential version of the real spectrum of a differential ring containing Q; an Artin-Schreier theory for such rings; the model theory of ordered differential fields. Results include: an algebraic characterization of the differential inequalities which are consequences of a given finite set of algebraic differential equations and inequalities; a differential counterpart of the Hormander-Lojasiewicz inequality.     

Algebraic geometry over algebraic structures. II. Foundations

In this paper, we introduce elements of algebraic geometry over an arbitrary algebraic structure. We prove so-called unification theorems that describe coordinate algebras of algebraic sets in several different ways.