Expansions of dense linear orders with the intermediate value property

In this paper, some new properties and results about Intermediate Value Property (IVP) via nonstandard concepts are given, and modifying some existing results to show the advantage role of nonstandard analysis tools for obtaining differed nonstandard distinguished results

On taking the intermediate value theorem (IVT) and its converse as a point of departure, this paper connects the intermediate value property (IVP) to the continuity postulate typically assumed in mathematical economics, and to the solvability axiom typically assumed in mathematical psychology. This connection takes the form of four portmanteau theorems, two for functions and the other two for binary relations, that give a synthetic and novel overview of the subject. In supplementation, the paper also surveys the antecedent literature both on the IVT itself, as well as its applications in economic and decision theory. The work underscores how a humble theorem, when viewed in a broad historical frame, bears the weight of many far-reaching consequences; and testifies to a point of view that the apparently complicated can sometimes be under-girded by a most basic and simple execution.

Introduction. These notes were originally written for a tutorial I gave in a Modnet Summer meeting which took place in Oxford 2006. I later gave a similar tutorial in the Wroclaw Logic colloquium 2007. The goal was to survey recent work in model theory of o-minimal structures, centered around the solution to a beautiful conjecture of Pillay on definable groups in o-minimal structures. The conjecture (which is now a theorem in most interesting cases) suggested a connection between arbitrary definable groups in o-minimal structures and compact real Lie groups.

We prove Zilber’s Trichotomy Conjecture for strongly minimal expansions of 2-dimensional groups, definable in o-minimal structures: Theorem. Let \mathcal{M} be an o-minimal expansion of a real closed field, \langle G;+\rangle a 2-dimensional group definable in \mathcal{M} , and \mathcal{D}=\langle G;+,\ldots\rangle a strongly minimal structure, all of whose atomic relations are definable in \mathcal{M} . If \mathcal{D} is not locally modular, then an algebraically closed field K is interpretable in \mathcal{D} , and the group G , with all its induced \mathcal{D} -structure, is definably isomorphic in \mathcal{D} to an algebraic K -group with all its induced K -structure.

Let (M, ≤,…) denote a Boolean ordered o-minimal structure. We prove that a Boolean subalgebra of M determined by an algebraically closed subset contains no dense atoms. We show that Boolean algebras with finitely many atoms do not admit proper expansions with o-minimal theory. The proof involves decomposition of any definable set into finitely many pairwise disjoint cells, i.e., definable sets of an especially simple nature. This leads to the conclusion that Boolean ordered structures with o-minimal theories are essentially bidefinable with Boolean algebras with finitely many atoms, expanded by naming constants. We also discuss the problem of existence of proper o-minimal expansions of Boolean algebras.

It is proved that any O-minimal structure M (in which the underlying order is dense) is strongly O-minimal (namely, every N elementarily equivalent to M is O-minimal).It is simultaneously proved that if M is 0minimal, then every definable set of n-tuples of M has finitely many "definably connected components."0. Introduction.In this paper we study the structure of definable sets (of tuples) in an arbitrary O-minimal structure M (in which the underlying order is dense).Recall from [PSI, PS2] that the structure M is said to be O-minimal if M = (M, <, Ri)iei, where < is a total ordering on M and every definable (with parameters) subset of M is a finite union of points in M and intervals (a, b) where aE M or a = -co and b E M or b = +co.M is said to be strongly O-minimal if every N which is elementarily equivalent to M is O-minimal.We will always assume that the underlying order of M is a dense order with no first or least element.In this paper we also introduce the notion of a definable set X C Mn being definably connected, and we prove THEOREM 0.1.Let M be O-minimal.Then any definable X C Mn is a disjoint union of finitely many definably connected definable sets.THEOREM 0.2.If M is O-minimal, then M is strongly O-minimal.THEOREM 0.3.(a) Let M be O-minimal and let (p(xi,...,xn,yi,...,ym) be any formula of L (the language for M).Then there is K < uj such that for any b E Mm, the set <j>(x,b)M (= {5 E Mn:M t= 4>(a,b)}) has at most K definably connected components.(b) If M is a O-minimal expansion o/(R, <), then in (a) we can replace definably connected by connected.Theorems 0.1 and 0.2 are proved simultaneously by a rather complicated induction argument (outlined in §3 and undertaken in § §4 and 5).Theorem 0.3 follows from Theorems 0.1 and 0.2 by a compactness argument.Let us remark that if M is the field of real numbers, or more generally any real closed field, then by Tarski's quantifier elimination [T], M is (strongly) O-minimal and moreover the definable sets (of n-tuples) in M are precisely the semialgebraic

1: Structures. 1.1. Structures. 1.2. Sentences. 1.3. Embeddings. 1.4. The Compactness Theorem. 1.5. Elementary classes and theories. 1.6. Complete theories. 1.7. Definable sets. 1.8. References. 2: Quantifier Elimination. 2.1. Elimination sets. 2.2. Discrete linear orders. 2.3. Dense linear orders. 2.4. Algebraically closed fields (and Tarski). 2.5. Tarski again: Real closed fields. 2.6. pp-elimination of quantifiers and modules. 2.7. Strongly minimal theories. 2.8. o-minimal theories. 2.9. Computational aspects of q. e. 2.10. References. 3: Model Completeness. 3.1. An introduction. 3.2. Abraham Robinson's test. 3.3. Model completeness and algebra. 3.4. p-adic fields and Artin's conjecture. 3.5. Existentially closed fields. 3.6. DCF0. 3.7. SCFp and DCFp. 3.8. ACFA. 3.9. References. 4: Elimination of Imaginaries. 4.1. Interpretability. 4.2. Imaginary elements. 4.3. Algebraically closed fields. 4.4. Real closed fields. 4.5. The elimination of imaginaries sometimes fails. 4.6. References. 5: Morley Rank. 5.1. A tale of two chapters. 5.2. Definable sets. 5.3. Types. 5.4. Saturated models. 5.5. A parenthesis: pure injective models. 5.6. Omitting types. 5.7. The Morley rank, at last. 5.8. Strongly minimal sets. 5.9. Algebraic closure and definable closure. 5.10. References. 6: Omega-stability. 6.1. Totally transcendental theories. 6.2. omega-stable groups. 6.3. omega-stable fields. 6.4. Prime models. 6.5. DCF0 revisited. 6.6. Ryll-Nardzewski's Theorem and other things. 6.7. References. 7: Classifying. 7.1. Shelah's Classification Theory. 7.2. Simple theories. 7.3. Stable theories. 7.4. Superstable theories. 7.5. w-stable theories. 7.6. Classifiable theories. 7.7. Shelah's Uniqueness Theorem. 7.8. Morley's Theorem. 7.9. Biinterpretability and Zilber Conjecture. 7.10. Two algebraic examples. 7.11. References. 8: Model Theory and Algebraic Geometry. 8.1. Introduction. 8.2. Algebraic varieties, ideals, types. 8.3. Dimension and Morley rank. 8.4. Morphisms and definable functions. 8.5. Manifolds. 8.6. Algebraic groups. 8.7. The Mordell-Lang Conjecture. 8.8. References. 9: O-Minimality. 9.1. Introduction. 9.2. The Monotonicity Theorem. 9.3. Cells. 9.4. Cell decomposition and other theorems. 9.5. Their proofs. 9.6. Definable groups in o-minimal structures. 9.7. O-minimality and Real Analysis. 9.8. Variants on the o-minimal theme. 9.9. No rose without thorns. 9.10. References. Bibliography. Index.

Part 1 The Real Numbers: The Real Number System Upper and Lower Bounds. Part 2 Sequences and Series: Algebraic Operations on Limits Monotone Sequences Infinite Series. Part 3 Continuous Functions: Functions, Limits and Continuity The Intermediate Value Property for Continuous Functions Uniform Continuity Increasing Functions. Part 4 Differentiable Functions: Repeated Differentiation Mean Value Theorems Local Maxima and Minima Taylor's Theorem. Part 5 Further Results on Infinite Series: Tests for Convergence Series of Complex Terms Power Series Multiplication of Series. Part 6 Special Functions: The Exponential Function The Logarithm Trigonometric Functions Inverse Trigonometric Functions. Part 7 The Riemann Integral: Integral Forms of the Mean Value Theorems Integration Over Unbounded Intervals Integration of Unbounded Functions. Part 8 The Number Pi.

We study how the propagation speed of interfaces in the Allen-Cahn phase field model for phase transformations in solids consisting of the elasticity equations and the Allen-Cahn equation depends on two parameters of the model. The two parameters control the interface energy and the interface width but change also the interface speed. To this end we derive an asymptotic expansion of second order for the interface speed, called the kinetic relation, and prove that it is uniformly valid in both parameters. As a consequence we show that the model error is proportional to the interface width divided by the interface energy. We conclude that simulations of interfaces with low interface energy based on this model require a very small interface width, implying a large numerical effort. Effective simulations thus need adaptive mesh refinement or other advanced techniques. This version of the paper contains the proofs of Theorem 4.5 and Lemma 5.8, which are omitted in the version published in Continuum Mechanics and Thermodynamics.

In this paper, we first try to solve the following problem: If a pluriharmonic function $f$ is definable in an arbitrary o-minimal expansion of the structure of the real field $\overline{\mathbb{R}}:=(\mathbb{R},+,-,.,0,1,&lt;)$, does this function be locally the real part of a holomorphic function which is definable in the same expansion? In Proposition 2.1 below, we prove that this problem has a positive answer if the Weierstrass division theorem holds true for the system of the rings of real analytic definable germs at the origin of $\mathbb{R}^n$. We obtain the same answer for an o-minimal expansion of the real field which is pfaffian closed (Proposition 2.6) for the harmonic functions. In the last section, we are going to show that the Weierstrass division theorem does not hold true for the rings of germs of real analytic functions at $0\in\mathbb{R}^n$ which are definable in the o-minimal structure $(\overline{\mathbb{R}}, x^{\alpha_1},\ldots,x^{\alpha_p})$, here $\alpha_1,\ldots,\alpha_p$ are irrational real numbers.

An argument of A. Borel [Bor-61, Proposition 3.1] shows that every compact connected Lie group is homeomorphic to the Cartesian product of its derived subgroup and a torus. We prove a parallel result for definably compact definably connected groups definable in an o-minimal expansion of a real closed field. As opposed to the Lie case, however, we provide an example showing that the derived subgroup may not have a definable semidirect complement.

Let M be an o-minimal structure or a p-adically closed field. Let be the space of complete n-types over M equipped with the following topology: The basic open sets of are of the form Ũ = {p ∈ Sn (M): U ∈ p} for U an open definable subset of Mn. is a spectral space. (For M = K a real closed field, is precisely the real spectrum of K[X1, …, Xn]; see [CR].) We will equip with a sheaf of LM-structures (where LM is a suitable language). Again for M a real closed field this corresponds to the structure sheaf on (see [S]). Our main point is that when Th(M) has definable Skolem functions, then if p ∈ , it follows that M(p), the definable ultrapower of M at p, can be factored through Mp, the stalk at p with respect to the above sheaf. This depends on the observation that if M ≺ N, a ∈ Nn and f is an M-definable (partial) function defined at a, then there is an open M-definable set U ⊂ Nn with a ∈ U, and a continuous M-definable function g:U → N such that g(a) = f(a).In the case that M is an o-minimal expansion of a real closed field (or M is a p-adically closed field), it turns out that M(p) can be recovered as the unique quotient of Mp which is an elementary extension of M.

Let $K,R$ be an algebraically closed field (of characteristic zero) and a real closed field respectively with $K=R(\sqrt{-1}).$ We show that every $K$-analytic set definable in an o-minimal expansion of $R$ can be locally approximated by a sequence of $K$

The Marker-Steinhorn Theorem (cf. [2] and [3]), says the following. If T is an o-minimal theory and M ≺ N is an elementary extension of models of T such that M is Dedekind complete in N, then for every N-definable subset X of Nk, the trace X ∩ Mk is M-definable. The original proof in [2] gives an explicit method how to construct a defining formula of X ∩ Mk out of a defining formula of X. A geometric reformulation of the Marker-Steinhorn Theorem is the definability of Hausdorff limits of families of definable sets. An explicit construction of these Hausdorff limits for expansions of the real field has recently been achieved in [1]. Both proofs and also the treatment [3] are technically involved.Here we give a short algebraic, but not constructive proof, if T is an expansion of real closed fields. In fact we'll identify the statement of the Theorem with a valuation theoretic property of models of T (namely condition (†) below). Therefore our proof might be applicable to other elementary classes which expand fields, if a notion of dimension and a reasonable valuation theory are available.From now on, let T be an o-minimal expansion of real closed fields. We have to show the following (cf. [2], Th. 2.1. for this formulation). If M is a model of T and p is a tame n-type over M (i.e., M is Dedekind complete in M ⟨ᾱ⟩ := dcl(Mᾱ) for some realization ᾱ of p), then p is a definable type (cf. [4], 11 .b).

1·1. A group is called characteristically simple if it has no proper non-trivial subgroups which are left invariant by all of its automorphisms. One familiar class of characteristically simple groups consists of all direct powers of simple groups: this contains all finite characteristically simple groups, and, more generally, all characteristically simple groups having minimal normal subgroups. However not all characteristically simple groups lie in this class because, for instance, additive groups of fields are characteristically simple. Our object here is to construct finitely generated groups, and also groups satisfying the maximal condition for normal subgroups, which are characteristically simple but which are not direct powers of simple groups.