Comments on “On the Indefinite Quadratic Fractional Optimization with Two Quadratic Constraints”

In this note, with reference to a paper by the same authors, we add an extra assumption, correct the statement of Lemma 2.1 and subsequently correct the proof of this lemma.     

Measure theory and weak König's lemma

We develop measure theory in the context of subsystems of second order arithmetic with restricted induction. We introduce a combinatorial principleWWKL (weak-weak König's lemma) and prove that it is strictly weaker thanWKL (weak König's lemma). We show thatWWKL is equivalent to a formal version of the statement that Lebesgue measure is countably additive on open sets. We also show thatWWKL is equivalent to a formal version of the statement that any Borel measure on a compact metric space is countably additive on open sets.The research of both authors was partially supported by NSF Grant DMS-8701481.     

Pointwise estimation of the difference of the solutions of a controlled functional operator equation in Lebesgue spaces

For a functional operator equation in Lebesgue space, we prove a statement on the pointwise estimate of the modulus of the increment of its global (on a fixed set Π ? ? ⁿ ) solution under the variation of the control function appearing in this equation. As an auxiliary statement, we prove a generalization of Gronwall’s lemma to the case of a nonlinear operator acting in Lebesgue space. The approach used here is based onmethods from the theory of stability of existence of global solutions to Volterra operator equations.     

A matrix Kronecker lemma

We show that a standard tool of probability theory, the Kronecker lemma, has matrix generalizations, but that one of these matrix generalizations is unsatisfactory, to the extent that unless certain extra conditions are placed on the matrix sequence appearing in the lemma statement, the lemma may fail to be true.     

Hilbert versus Hindman

We show that a statement HIL, which is motivated by a lemma of Hilbert and close in formulation to Hindman’s theorem, is actually much weaker than Hindman’s theorem. In particular, HIL is finitistically reducible in the sense of Hilbert’s program, while Hindman’s theorem is not.     

On the KŁR conjecture in random graphs

The K?R conjecture of Kohayakawa, ?uczak, and Rödl is a statement that allows one to prove that asymptotically almost surely all subgraphs of the random graph G _n,p , for sufficiently large p:= p(n), satisfy an embedding lemma which complements the sparse regularity lemma of Kohayakawa and Rödl. We prove a variant of this conjecture which is sufficient for most known applications to random graphs. In particular, our result implies a number of recent probabilistic versions, due to Conlon, Gowers, and Schacht, of classical extremal combinatorial theorems. We also discuss several further applications.     

ON THE METRIZATION LEMMA FOR UNIFORM SPACES

Abstract

We show a numeric generalization of the well-known metrization lemma for uniform spaces, thereby answering a question left open in [2] to the affirmative. An application of the new lemma in the setting of approach theory yields the conclusion that every approach uniformity has a basis of pseudo-metrics.     

A note on the complexity of determining optimal strategies in games with common payoffs

In a recent paper [Int J Game Theory (2001) 30:99–106], Chu and Halpern investigated the problem of finding optimal strategies in certain games with common payoffs. This short technical note answers a computational complexity question that was left open in their paper. Acknowledgement.I thank the referee for a very careful reading of the paper, and for pointing out to me a number of typos and inconsistencies in an earlier version of the paper.     

Common extension of bilateral series for Andrews’ q-Bailey and q-Gauss sums

By means of the modified Abel lemma on summation by parts, we establish a common bilateral series extension of the q-Bailey and q-Gauss sums discovered by Andrews (Duke Math. J. 40 (1973), 525–528).     

The ring lemma in three dimensions

Suppose that n cyclically tangent discs with pairwise disjoint interiors are externally tangent to and surround the unit disc. The sharp ring lemma in two dimensions states that no disc has a radius below c _n (R ²) = (F _2n−3−1)⁻¹—where F _k denotes the kth Fibonacci number—and that the lower bound is attained in essentially unique Apollonian configurations. In this article, generalizations of the ring lemma to three dimensions are discussed, a version of the ring lemma in three dimensions is proved, and a natural generalization of the extremal two-dimensional configuration—thought to be extremal in three dimensions—is given. The sharp three-dimensional ring lemma constant of order n is shown to be bounded from below by the two-dimensional constant of order n − 1.     

Singularity and decay estimates for the conformal k-hessian equation via Liouville-type theorems

We study some connections between Liouville type theorems and local properties of nonnegative solutions to conformal k-hessian equations by making use of an elementary lemma for all positive functions in Li and Zhang (J. Anal. Math. 90 (2003), 27–87) and related Liouville type theorems in Li and Li (Acta. Math. 195 (2005), 117–154). Research of the second author is supported by Tianyuan Fund of Mathematics (10826061).     

Remarks on fully nonlinear equations associated with doubling lemma

ABSTRACT

In this paper, we present applications of the doubling lemma to nonlinear equations, including a k-Hessian equation and an integral equation of Wolff-type.     

On meromorphic continuation in a fixed direction

In the present paper, we prove a local boundary version of the well-known Rothstein lemma about the meromorphic continuation with respect to one of the complex variables. The statement is simple, and the proof is based on the well-known Hadamard formulas for the radii of meromorphy, on recent results of Imomkulov about the boundary properties of sequences of plurisubharmonic functions, and on the Rothstein lemma.     

Fibration de Hitchin et endoscopie

We propose a geometric interpretation of the theory of elliptic endoscopy, due to Langlands and Kottwitz, in terms of the Hitchin fibration. As applications, we prove a global analog of a purity conjecture, due to Goresky, Kottwitz and MacPherson. For unitary groups, this global purity statement has been used, in a joint work with G. Laumon, to prove the fundamental lemma over a local fields of equal characteristics.      

A remark on the incomparability of two criteria for a uniform convergence of probability measures

Summary This paper connects with Theorem 3 of the author’s paper [1], in which two criteria for type (B) _d convergence ([3]) are shown to be incomparable to each other by presenting two examples. However, the statement of the theorem is not complete. In the present paper, we shall modify the statement of the theorem and give a proof by presenting a new example.     

Gröbner–Shirshov Bases: From their Incipiency to the Present

In this paper, the history and the main results of the theory of Gröbner–Shirshov bases are given for commutative, noncommutative, Lie, and conformal algebras from the beginning (1962) to the present time. The problem of constructing a base of a free Lie algebra is considered, as well as the problem of studying the structure of free products of Lie algebras, the word problem for Lie algebras, and the problem of embedding an arbitrary Lie algebra into an algebraically closed one. The modern form of the composition-diamond lemma (the CD lemma) is presented. The rewriting systems for groups are considered from the point of view of Gröbner–Shirshov bases. The important role of conformal algebras is treated, the statement of the CD lemma for associative conformal algebras is given, and some examples are considered. An analog of the Hilbert basis theorem for commutative conformalalgebras is stated. Bibliography: 173 titles.     

Existence and asymptotical behavior of the minimizer of Hartree type equation with periodic potentials

ABSTRACT

In the present paper, we consider Hartree type equation with periodic potential. On the one hand, we prove the existence and nonexistence of the minimizer for the energy functional by using concentration-compactness lemma. On the other hand, we prove the energy estimates and describe the asymptotical behavior of the minimizer     

More on the Strength of Engeler’s Lemma

We introduce semilattices equipped with a partial n-ary operation ρ. A useful separation lemma for such nontrivial complete partial ρ-semilattices is proved equivalent to PIT, the prime ideal theorem. The relation of various versions of the Lemma to each other and to PIT is also explored. Supported by the Ministry of Education of the Czech Republic under the project MSM0021622409.     

On the symmetric square Unstable twisted characters

We provide a purely local computation of the (elliptic) twisted (by “transpose-inverse”) character of the representationπ=I(1) of PGL(3) over ap-adic field induced from the trivial representation of the maximal parabolic subgroup. This computation is independent of the theory of the symmetric square lifting of [IV] of automorphic and admissible representations of SL(2) to PGL(3). It leads — see [FK] — to a proof of the (unstable) fundamental lemma in the theory of the symmetric square lifting, namely that corresponding spherical functions (on PGL(2) and PGL(3)) are matching: they have matching orbital integrals. The new case in [FK] is the unstable one. A direct local proof of the fundamental lemma is given in [V].     

The Speciality Lemma, Rank 2 Bundles and Gherardelli-type Theorems for Surfaces in P 4

In the present paper we give a very short and easy proof of the speciality lemma for codimension 2 subvarieties, even those that are reducible or non-reduced, in P ⁿ . Furthermore we give cohomological conditions that force a subcanonical surface in P ⁴ to be a complete intersection and a rank 2 bundle to split, which generalize the classical First Theorem of Gherardelli.