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Working paper

Bachet's game is a variant of the game of Nim. There are n objects in one pile. Two players make moves one after another. On every move, a player is allowed to take any positive number of objects not exceeding some fixed number m. The player who takes the last object loses. We consider a variant of Bachet's game in which each move is a lottery over set {1,2,…,m}. Outcome of a lottery is the number of objects that player takes from the pile. We show that under some nondegenericity assumptions on the set of available lotteries the probability that the first player wins in subgame perfect Nash equilibrium converges to 1/2 as n tends to infinity.

Added: Mar 22, 2019

Working paper

We get sufficient conditions for the full basic automorphism group of a complete
Cartan foliation to admit a unique (finite-dimensional) Lie group structure in the category
of Cartan foliations. In particular, we obtain sufficient conditions for this group
to be discrete. Emphasize that the transverse Cartan geometry may be noneffective.
Some estimates of the dimension of this group depending on the transverse geometry
are found. Further, we investigate Cartan foliations covered by fibrations and ascertain
their specification. Examples of computing the full basic automorphism group of
complete Cartan foliations are constructed.

Added: Nov 10, 2014

Working paper

Exploring Bass' Triangulability Problem on unipotent algebraic subgroups of the affine Cremona groups, we prove a triangulability criterion, the existence of nontriangulable connected solvable affine algebraic subgroups of the Cremona groups, and stable triangulability of such subgroups; in particular, in the stable range we answer Bass' Triangulability Problem is the affirmative. To this end we prove a theorem on invariant subfields of $1$-extensions. We also obtain a general construction of all rationally triangulable subgroups of the Cremona groups and, as an application, classify rationally triangulable connected one-dimensional unipotent affine algebraic subgroups of the Cremona groups up to conjugacy.

Added: Apr 16, 2015

Working paper

It was shown in our previous paper that quantum ${\rm gl}_N$ $R$-matrices
satisfy noncommutative analogues of the Fay identities in ${\rm gl}_N^{\otimes
3}$. In this paper we extend the list of $R$-matrix valued elliptic function
identities. We propose counterparts of the Fay identities in ${\rm
gl}_N^{\otimes 2}$, the symmetry between the Planck constant and the spectral
parameter, quasi-periodicities with respect to these variables, the Kronecker
double series representation of the R-matrix. As an application we construct
$R$-matrix valued $2N^2\times 2N^2$ Lax pairs for the Painlev\'e VI equation
(in the elliptic form) with four free constants using ${\mathbb Z}_N\times
{\mathbb Z}_N$ elliptic $R$-matrix. More precisely, the four free constants
case appears for an odd $N$ while even $N$'s correspond to a single constant.

Added: Feb 3, 2015

Working paper

We propose a non-commutative generalization of Beilinson's Conjecture on the regulator map from algebraic K-theory to Deligne cohomology of algebraic varieties over Q. We also check a baby case of the generalized conjecture, namely, the case of finite-dimensional associative algebras.

Added: Dec 22, 2013

Working paper

We compute the spaces of sections of powers of the determinant line bundle on the spherical Schubert subvarieties of the Beilinson- Drinfeld affine Grassmannians. The answer is given in terms of global Demazure modules of the current Lie algebra.

Added: Apr 2, 2020

Working paper

We prove that every quasi-smooth hypersurface in the 95 families of weighted Fano threefold hypersurfaces is birationally rigid.

Added: Dec 27, 2013

Working paper

According to the classical theorem, every irreducible algebraic variety endowed with a nontrivial rational action of a connected linear algebraic group is birationally isomorphic to a product of another algebraic variety and the s-dimensional projectice space with positive s. We show that the classical proof of this theorem actually works only in characteristic 0 and we give a characteristic free proof of it. To this end we prove and use a characterization of connected linear algebraic groups G with the property that every rational action of G on an irreducible algebraic variety is birationally equivalent to a regular action of G on an affine algebraic variety.

Added: Feb 10, 2015

Working paper

We give a simple construction of the correspondence between square-zero extensions R′ of a ring R by an R-bimodule M and second MacLane cohomology classes of R with coefficients in M (the simplest non-trivial case of the construction is R=M=Z/p, R′=Z/p2, thus the Bokstein homomorphism of the title). Following Jibladze and Pirashvili, we treat MacLane cohomology as cohomology of non-additive endofunctors of the category of projective R-modules. We explain how to describe liftings of R-modules and complexes of R-modules to R′ in terms of data purely over R. We show that if R is commutative, then commutative square-zero extensions R′ correspond to multiplicative extensions of endofunctors. We then explore in detail one particular multiplicative non-additive endofunctor constructed from cyclic powers of a module V over a commutative ring R annihilated by a prime p. In this case, R′ is the second Witt vectors ring W2(R) considered as a square-zero extension of R by the Frobenius twist R(1).

Added: Nov 20, 2015

Working paper

In this article, we extend the phenomena of a bony attractor from a rather artificial class of step skew products to the class of diffeomorphisms on the Cartesian product of the two-dimensional torus by a sphere of arbitrary dimension.

Added: May 16, 2013

Working paper

In this article we prove in a new way that a generic polynomial vector field in ℂ² possesses countably many homologically independent limit cycles. The new proof needs no estimates on integrals, provides thinner exceptional set for quadratic vector fields, and provides limit cycles that stay in a bounded domain.

Added: Apr 15, 2015

Working paper

We prove that b2 is bounded for hyperk¨ahler manifolds with vanishing odd-Betti numbers. The explicit upper boundary is conjectured. Following the method described by Sawon we prove that b2 is bounded in dimension eight and ten in the case of vanishing odd-Betti numbers by 24 and 25 respectively.

Added: Nov 15, 2015

Working paper

We study algebras constructed by quantum Hamiltonian reduction associated with symplectic quotients of symplectic vector spaces, including deformed preprojective algebras, symplectic reflection algebras (rational Cherednik algebras), and quantization of hypertoric varieties introduced by Musson and Van den Bergh. We determine BRST cohomologies associated with these quantum Hamiltonian reductions. To compute these BRST cohomologies, we make use of method of deformation quantization (DQ-algebras) and F-action studied in [Kashiwara-Rouquier], and in [Gordon-Losev].

Added: Feb 16, 2015

Working paper

We discuss Calabi–Yau and fractional Calabi–Yau semiorthogonal components of derived categories of coherent sheaves on smooth projective varieties. The main result is a general construction of a fractional Calabi–Yau category from a rectangular Lefschetz decomposition and a spherical functor. We give many examples of application of this construction and discuss some general properties of Calabi–Yau categories.

Added: Nov 15, 2015

Working paper

We construct the reduction of an exact category with a twist functor with respect to an element of its graded center in presence of an exact-conservative forgetful functor annihilating this central element. The procedure allows, e.g., to recover the abelian/exact category of modular representations of a finite group from the exact category of its l-adic representations. The construction uses matrix factorizations in a nontraditional way. We obtain the Bockstein long exact sequences for the Ext groups in the exact categories produced by reduction. Our motivation comes from the theory of Artin--Tate motives and motivic sheaves with finite coefficients, and our key techniques generalize those of Section 4 in the author's paper "Mixed Artin-Tate motives with finite coefficients".

Added: Apr 22, 2014

Working paper

Bergh D.,

, et al. arxiv.org. math. Cornell University, 2017
Added: Oct 17, 2017

Working paper

We show that the derived category of any singularity over a field of characteristic 0 can be embedded fully and faithfully into a smooth triangulated category which has a semiorthogonal decomposition with components equivalent to derived categories of smooth varieties. This provides a categorical resolution of the singularity.

Added: Oct 4, 2013

Working paper

We establish the analogue of the Cayley--Hamilton theorem for the quantum matrix algebras of the symplectic type.

Added: Jan 26, 2021

Working paper

We consider the class C(T) of continuous real-valued functions on the circle. For certain classes of functions naturally characterised by the rapidity of decrease of Fourier coefficients we investigate whether it is possible to bring families of functions in C(T) into these classes by a change of variable. This paper was originally published in Matematicheskii Sbornik, 181:8 (1990), 1099--1113 (Russian). The English translation, published in Mathematics of the USSR, Sbornik, 70:2 (1991), 541--555, is to a large extent inconsistent with the original text. Herein the author provides a corrected translation.

Added: Sep 8, 2015

Working paper

Added: Feb 6, 2013

Working paper

We prove that the characteristic foliation F on a non- singular divisor D in an irreducible projective hyperkaehler mani- fold X cannot be algebraic, unless the leaves of F are rational curves or X is a surface. More generally, we show that if X is an arbitrary projective manifold carrying a holomorphic symplectic 2-form, and D and F are as above, then F can be algebraic with non-rational leaves only when, up to a finite etale cover, X is the product of a symplectic projective manifold Y with a symplectic surface and D is the pull-back of a curve on this surface. When D is of general type, the fact that F cannot be algebraic unless X is a surface was proved by Hwang and Viehweg. The main new ingredient for our results is the observation that the canonical bundle of the orbifold base of the family of leaves must be torsion. This implies, in particular, the isotriviality of the family of leaves of F . ́

Added: May 10, 2014