Infinitely Peano differentiable functions in polynomially bounded o-minimal structures

Let R be an o-minimal expansion of a real closed field. We show that the definable infinitely Peano differentiable functions are smooth if and only if R is polynomially bounded.     

Locally polynomially bounded structures

We prove a theorem which provides a method for constructingpoints on varieties defined by certain smooth functions. Werequire that the functions be definable in a definably completeexpansion of a real closed field and be locally definable ina fixed o-minimal and polynomially bounded reduct. As an applicationwe show that in certain o-minimal structures, definable functionsare piecewise implicitly defined over the basic functions inthe language.     

The Field of Reals with Multisummable Series and the Exponential Function

We show that the field of real numbers with multisummable realpower series is model complete, o-minimal and polynomially bounded.Further expansion by the exponential function yields again amodel complete and o-minimal structure which is exponentiallybounded, and in which the Gamma function on the positive realline is definable. 2000 Mathematics Subject Classification:primary 03C10, 32B05, 32B20; secondary, 26E05.     

Uniformly locally o-minimal structures and locally o-minimal structures admitting local definable cell decomposition

We define and investigate a uniformly locally o-minimal structure of the second kind in this paper. All uniformly locally o-minimal structures of the second kind have local monotonicity, which is a local version of monotonicity theorem of o-minimal structures. We also demonstrate a local definable cell decomposition theorem for definably complete uniformly locally o-minimal structures of the second kind. We define dimension of a definable set and investigate its basic properties when the given structure is a locally o-minimal structure which admits local definable cell decomposition.     

Some definable properties of sets in non-valuational weakly o-minimal structures

Let \({\mathcal {M}}=(M,<,+,\cdot ,\ldots )\) be a non-valuational weakly o-minimal expansion of a real closed field \((M,<,+,\cdot )\). In this paper, we prove that \({\mathcal {M}}\) has a \(C^r\)-strong cell decomposition property, for each positive integer r, a best analogous result from Tanaka and Kawakami (Far East J Math Sci (FJMS) 25(3):417–431, 2007). We also show that curve selection property holds in non-valuational weakly o-minimal expansions of ordered groups. Finally, we extend the notion of definable compactness suitable for weakly o-minimal structures which was examined for definable sets (Peterzil and Steinhorn in J Lond Math Soc 295:769–786, 1999), and prove that a definable set is definably compact if and only if it is closed and bounded.     

A matching problem with side conditions

Given a graph G, a 2-matching is an assignment of nonnegative integers to the edges of G such that for each node i of G, the sum of the values on the edges incident with i is at most 2. A triangle-free 2-matching is a 2-matching such that no cycle of size 3 in G has the value 1 assigned to all of its edges. In this paper we describe explicity the convex hull of triangle-free 2-matchings by means of its extreme points and of its facets. We give a polynomially bounded algorithm which maximizes a linear function over the set of triangle-free 2-matchings. Finally we discuss some related problems.     

Polynomially bounded cohomology and discrete groups

We establish the homological foundations for studying polynomially bounded group cohomology, and show that the natural map from PH^*(G;Q) to H^*(G;Q) is an isomorphism for a certain class of groups.     

On lovely pairs of geometric structures

We study the theory of lovely pairs of geometric structures, in particular o-minimal structures. We use the pairs to isolate a class of geometric structures called weakly locally modular which generalizes the class of linear structures in the settings of SU-rank one theories and o-minimal theories. For o-minimal theories, we use the Peterzil-Starchenko trichotomy theorem to characterize for a sufficiently general point, the local geometry around it in terms of the thorn U-rank of its type inside a lovely pair.     

Witt groups and the elementary type conjecture

Let A be an algebra with involution * over a field F of characteristic zero and Id(A, *) the ideal of the free algebra with involution of *-identities of A. By means of the representation theory of the hyperoctahedral group Z ₂wrS _n we give a characterization of Id(A, *) in case the sequence of its *-codimensions is polynomially bounded. We also exhibit an algebra G ₂ with the following distinguished property: the sequence of *-codimensions of Id(G ₂, *) is not polynomially bounded but the *-codimensions of any T-ideal U properly containing Id(G ₂, *) are polynomially bounded.     

Compact domination for groups definable in linear o-minimal structures

We prove the Compact Domination Conjecture for groups definable in linear o-minimal structures. Namely, we show that every definably compact group G definable in a saturated linear o-minimal expansion of an ordered group is compactly dominated by (G/G ⁰⁰, m, π), where m is the Haar measure on G/G ⁰⁰ and π : G → G/G ⁰⁰ is the canonical group homomorphism.     

Closure and connected component of a planar global semianalytic set defined by analytic functions definable in o-minimal structure

We consider a global semianalytic set defined by real analytic functions definable in an o-minimal structure. When the o-minimal structure is polynomially bounded, we show that the closure of this set is a global semianalytic set defined by definable real analytic functions. We also demonstrate that a connected component of a planar global semianalytic set defined by real analytic functions definable in a substructure of the restricted analytic field is a global semianalytic set defined by definable real analytic functions.     

A constant bound for the periods of parallel chip-firing games with many chips

We prove that any parallel chip-firing game on a graph G with at least 4|E(G)| − |V(G)| chips stabilizes, i.e., such a game has eventual period of length 1. Furthermore, we obtain a polynomial bound on the number of rounds before stabilization. This result is a counterpoint to previous results which showed that the eventual periods of parallel chip-firing games with few chips need not be polynomially bounded.     

on the o-minimal LS-category

We introduce the o-minimal LS-category of definable sets in o-minimal expansions of ordered fields and we establish a relation with the semialgebraic and the classical one. We also study the o-minimal LS-category of definable groups. Along the way, we show that two definably connected definably compact definable groups G and H are definable homotopy equivalent if and only if L(G) and L(H) are homotopy equivalent, where L is the functor which associates to each definable group its corresponding Lie group via Pillay’s conjecture.     

Weakly o-minimal expansions of ordered fields of finite transcendence degree

Using a work of Diaz concerning algebraic independence of certainsequences of numbers, we prove that if K is a field of finitetranscendence degree over the rationals, then every weakly o-minimalexpansion of (K,,+,·) is polynomially bounded. In thespecial case where K is the field of all real algebraic numbers,we give a proof which makes use of a much weaker result fromtranscendental number theory, namely, the Gelfond–Schneidertheorem. Apart from this we make a couple of observations concerningweakly o-minimal expansions of arbitrary ordered fields of finitetranscendence degree over the rationals. The strongest resultwe prove says that if K is a field of finite transcendence degreeover the rationals, then all weakly o-minimal non-valuationalexpansions of (K,,+,·) are power bounded.     

Quasianalytic Denjoy-Carleman classes and o-minimality

We show that the expansion of the real field generated by the functions of a quasianalytic Denjoy-Carleman class is model complete and o-minimal, provided that the class satisfies certain closure conditions. Some of these structures do not admit analytic cell decomposition, and they show that there is no largest o-minimal expansion of the real field.

     

Valuation theory of exponential Hardy fields I

We describe the valuation theoretic properties of the Hardy fields associated to models of , where T is the theory of a polynomially bounded o-minimal expansion of the reals and is the real exponential function. We deduce that has levels with parameters and is exponentially bounded. We establish a maximality property of , the Hardy field of the expansion by the restricted analytic functions and power functions. Received: 10 July 2000 ; in final form: 15 April 2002/Published online: 24 February 2003 RID="*" ID="*" This paper was written while both authors were partially supported by a Canadian NSERC research grant.     

An infinite dimensional affine nil algebra with finite Gelfand-Kirillov dimension

The famous 1960's construction of Golod and Shafarevich yields infinite dimensional nil, but not nilpotent, algebras. However, these algebras have exponential growth. Here, we construct an infinite dimensional nil, but not locally nilpotent, algebra which has polynomially bounded growth.

     

The similarity problem for Fourier algebras and corepresentations of group von Neumann algebras

Let G be a locally compact group, and let A(G) and VN(G) be its Fourier algebra and group von Neumann algebra, respectively. In this paper we consider the similarity problem for A(G): Is every bounded representation of A(G) on a Hilbert space H similar to a *-representation? We show that the similarity problem for A(G) has a negative answer if and only if there is a bounded representation of A(G) which is not completely bounded. For groups with small invariant neighborhoods (i.e. SIN groups) we show that a representation π:A(G)→B(H) is similar to a *-representation if and only if it is completely bounded. This, in particular, implies that corepresentations of VN(G) associated to non-degenerate completely bounded representations of A(G) are similar to unitary corepresentations. We also show that if G is a SIN, maximally almost periodic, or totally disconnected group, then a representation of A(G) is a *-representation if and only if it is a complete contraction. These results partially answer questions posed in Effros and Ruan (2003) [7] and Spronk (2002) [25].     

Maximization of lower semi-continuous convex functional on bounded subsets of locally convex spaces. II: Quasi-Lagrangian duality theorems

We prove, for a proper lower semi-continuous convex functional ? on a locally convex space E and a bounded subset G of E, a formula for sup ?(G) which is symmetric to the Lagrange multiplier theorem for convex minimization, obtained in [7], with the difference that for sup ?(G) Lagrange multiplier functionals need not exist. When ? is also continuous we give some necessary conditions for g₀ ∈ G to satisfy ?(g₀) = sup ?(G). Also, we give some applications to deviations and farthest points. Finally, we show the connections with the “hyperplane theorems” of our previous paper [8].     

Some complexity problems on single input double output controllers

We investigate the time complexity of constructing single input double output state feedback controller structures, given the directed structure graph G of a system. Such a controller structure defines a restricted type of P₃-partition of the graph G. A necessary condition (∗) is described and some classes of graphs are identified where the search problem of finding a feasible P₃-partition is polynomially solvable and, in addition, (∗) is not only necessary but also sufficient for the existence of a P₃-partition. It is also proved that the decision problem on two particular graph classes — defined in terms of forbidden subgraphs — remains NP-complete, but is polynomially solvable on the intersection of those two classes. The polynomial-time solvability of some further related problems is shown, too.