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66
On the Combinatorial and Algebraic Complexity of Quantifier Elimination
, 1996
"... In this paper, a new algorithm for performing quantifier elimination from first order formulas over real closed fields is given. This algorithm improves the complexity of the asymptotically fastest algorithm for this problem, known to this date. A new feature of this algorithm is that the role of th ..."
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Cited by 201 (29 self)
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In this paper, a new algorithm for performing quantifier elimination from first order formulas over real closed fields is given. This algorithm improves the complexity of the asymptotically fastest algorithm for this problem, known to this date. A new feature of this algorithm is that the role of the algebraic part (the dependence on the degrees of the input polynomials) and the combinatorial part (the dependence on the number of polynomials) are separated. Another new feature is that the degrees of the polynomials in the equivalent quantifierfree formula that is output, are independent of the number of input polynomials. As special cases of this algorithm, new and improved algorithms for deciding a sentence in the first order theory over real closed fields, and also for solving the existential problem in the first order theory over real closed fields, are obtained.
Cherednik algebras and differential operators on quasiinvariants
 Duke Math. J
"... We develop representation theory of the rational Cherednik algebra Hc associated to a finite Coxeter group W in a vector space h, and a parameter “c. ” We use it to show that, for integral values of “c, ” the algebra Hc is simple and Morita equivalent to D(h)#W, the cross product of W with the algeb ..."
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Cited by 55 (14 self)
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We develop representation theory of the rational Cherednik algebra Hc associated to a finite Coxeter group W in a vector space h, and a parameter “c. ” We use it to show that, for integral values of “c, ” the algebra Hc is simple and Morita equivalent to D(h)#W, the cross product of W with the algebra of polynomial differential operators on h. O. Chalykh, M. Feigin, and A. Veselov [CV1], [FV] introduced an algebra, Qc, of quasiinvariant polynomials on h, such that C[h] W ⊂ Qc ⊂ C[h]. We prove that the algebra D(Qc) of differential operators on quasiinvariants is a simple algebra, Morita equivalent to D(h). The subalgebra D(Qc) W ⊂ D(Qc) of Winvariant operators turns out to be isomorphic to the spherical subalgebra eHce ⊂ Hc. We show that D(Qc) is generated, as an algebra, by Qc and its “Fourier dual ” Q ♭ c, and that D(Qc) is a rankone projective (Qc ⊗ Q ♭ c)module (via multiplicationaction on D(Qc) on opposite sides).
Algebraic Geometry
, 2002
"... Notes for a class taught at the University of Kaiserslautern 2002/2003 ..."
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Cited by 23 (0 self)
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Notes for a class taught at the University of Kaiserslautern 2002/2003
The completion theorem in Ktheory for proper actions of a discrete group
"... We prove a version of the AtiyahSegal completion theorem for proper actions of an infinite discrete group G. More precisely, for any finite proper GCWcomplex X, K (EG\Theta GX) is the completion of K G (X) with respect to a certain ideal. We also show, for such G and X, that KG (X) can be ..."
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Cited by 21 (5 self)
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We prove a version of the AtiyahSegal completion theorem for proper actions of an infinite discrete group G. More precisely, for any finite proper GCWcomplex X, K (EG\Theta GX) is the completion of K G (X) with respect to a certain ideal. We also show, for such G and X, that KG (X) can be defined as the Grothendieck group of the monoid of Gvector bundles over X. Key words: Ktheory, proper actions, vector bundles 1991 mathematics subject classification: primary 55N91, secondary 19L47 Let G be any discrete group. For such G, a GCWcomplex is a CWcomplex with G action which permutes the cells, such that an element g 2 G sends a cell to itself only by the identity map. A GCWcomplex X is proper if all of its isotropy subgroups have finite order, and is finite if it is made up of finitely many orbits of cells. A GCWpair is a pair of Gspaces (X; A), where X is a GCWcomplex and A is a Ginvariant subcomplex. The main results of this paper are Theorems 3.2 and 4.3 below...
Sheaves on Artin stacks
 J. Reine Angew. Math. (Crelle’s Journal
"... Abstract. We develop a theory of quasi–coherent and constructible sheaves on algebraic stacks correcting a mistake in the recent book of Laumon and MoretBailly. We study basic cohomological properties of such sheaves, and prove stack–theoretic versions of Grothendieck’s Fundamental Theorem for prop ..."
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Cited by 19 (1 self)
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Abstract. We develop a theory of quasi–coherent and constructible sheaves on algebraic stacks correcting a mistake in the recent book of Laumon and MoretBailly. We study basic cohomological properties of such sheaves, and prove stack–theoretic versions of Grothendieck’s Fundamental Theorem for proper morphisms, Grothendieck’s Existence Theorem, Zariski’s Connectedness Theorem, as well as finiteness Theorems for proper pushforwards of coherent and constructible sheaves. We also explain how to define a derived pullback functor which enables one to carry through the construction of a cotangent complex for a morphism of algebraic stacks due to Laumon and Moret–Bailly. 1.1. In the book ([LMB]) the lisseétale topos of an algebraic stack was introduced, and a theory of quasi–coherent and constructible sheaves in this topology was developed. Unfortunately, it was since observed by Gabber and Behrend (independently) that the lisseétale topos is not functorial as asserted in (loc. cit.), and hence the development of the theory of sheaves in this book is not satisfactory “as is”. In addition, since the publication of the book ([LMB]), several new results have been obtained such as finiteness of coherent and étale cohomology ([Fa], [Ol]) and various other consequences of Chow’s Lemma ([Ol]).
Krichever correspondence for algebraic varieties
 english translation in Izv. Math. 65 (2001
"... In the work is constructed new acyclic resolutions of quasicoherent sheaves. These resolutions is connected with multidimensional local fields. Then the obtained resolutions is applied for a construction of generalization of the Krichever map to algebraic varieties of any dimension. This map gives i ..."
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Cited by 14 (3 self)
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In the work is constructed new acyclic resolutions of quasicoherent sheaves. These resolutions is connected with multidimensional local fields. Then the obtained resolutions is applied for a construction of generalization of the Krichever map to algebraic varieties of any dimension. This map gives in the canonical way two ksubspaces B ⊂ k((z1))... ((zn)) and W ⊂ k((z1))... ((zn)) ⊕r from arbitrary algebraic ndimensional CohenMacaulay projective integral scheme X over a field k, a flag of closed integral subschemes X = Y0 ⊃ Y1 ⊃...Yn (such that Yi is an ample Cartier divisor on Yi−1, and Yn is a smooth kpoint on all Yi), formal local parameters of this flag in the point Yn, a rank r vector bundle F on X, and a trivialization F in the formal neighbourhood of the point Yn, where the ndimensional local field k((z1))... ((zn)) is associated with the flag Y0 ⊃... ⊃ Yn. In addition, the constructed map is injective, i. e., it is possible to reconstruct uniquely all the original geometrical data. Besides, from the subspace B is written explicitly a complex, which calculates cohomology of the sheaf OX on X; and from the subspace W is written explicitly a complex, which calculates cohomology of F on X. 1
Algorithms in Semialgebraic Geometry
, 1996
"... In this thesis we present new algorithms to solve several very general problems of semialgebraic geometry. These are currently the best algorithms for solving these problems. In addition, we have proved new bounds on the topological complexity of real semialgebraic sets, in terms of the paramete ..."
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Cited by 9 (0 self)
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In this thesis we present new algorithms to solve several very general problems of semialgebraic geometry. These are currently the best algorithms for solving these problems. In addition, we have proved new bounds on the topological complexity of real semialgebraic sets, in terms of the parameters of the polynomial system defining them, which improve some old and widely used results in this field. In the first part of the thesis we describe new algorithms for solving the decision problem for the first order theory of real closed fields and the more general problem of quantifier elimination. Moreover, we prove some purely mathematical theorems on the number of connected components and on the existence of small rational points in a given semialgebraic set. The second part of this thesis deals with connectivity questions of semialgebraic sets. We develop new techniques in order to give a...
Nonarchimedean analytification of algebraic spaces
 JOURNAL OF ALGEBRAIC GEOMETRY 18
, 2009
"... ..."
Branching rules for Hecke Algebras of Type Dn
, 2004
"... In this paper we study the branching problems for Hecke algebra H(Dn) of type Dn. We explicitly describe the decompositions of the socle of the restriction of each irreducible H(Dn)representation to H(Dn−1) into irreducible modules by using the corresponding results for type B Hecke algebras. In pa ..."
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Cited by 7 (2 self)
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In this paper we study the branching problems for Hecke algebra H(Dn) of type Dn. We explicitly describe the decompositions of the socle of the restriction of each irreducible H(Dn)representation to H(Dn−1) into irreducible modules by using the corresponding results for type B Hecke algebras. In particular, we show that any such restrictions are always multiplicity free. 1