Notes on the stability of separably closed fields

1979 ◽  
Vol 44 (3) ◽  
pp. 412-416 ◽  
Author(s):  
Carol Wood
Keyword(s):  
Differential Algebra ◽  
Complete Theory ◽  
Model Completeness ◽  
Closed Fields ◽  
Superstable Theories ◽  
Basic Facts ◽  
The Stability ◽  
Differential Fields

AbstractThe stability of each of the theories of separably closed fields is proved, in the manner of Shelah's proof of the corresponding result for differentially closed fields. These are at present the only known stable but not superstable theories of fields. We indicate in §3 how each of the theories of separably closed fields can be associated with a model complete theory in the language of differential algebra. We assume familiarity with some basic facts about model completeness [4], stability [7], separably closed fields [2] or [3], and (for §3 only) differential fields [8].

Differential Polynomials

2017 ◽  
Author(s):  
Matthias Aschenbrenner ◽  
Lou van den Dries ◽  
Joris van der Hoeven
Keyword(s):  
Characteristic Zero ◽  
Natural Setting ◽  
Differential Polynomials ◽  
Differential Field ◽  
Closed Fields ◽  
Basic Facts ◽  
Differential Fields

This chapter deals with differential polynomials. It first presents some basic facts about differential fields that are of characteristic zero with one distinguished derivation, along with their extensions. It then considers various decompositions of differential polynomials in their natural setting, along with valued differential fields and the property of continuity of the derivation with respect to the valuation topology. It also discusses the gaussian extension of the valuation to the ring of differential polynomials and concludes with some basic results on simple differential rings and differentially closed fields. In contrast to the corresponding notions for fields, the chapter shows that differential fields always have proper d-algebraic extensions, and the differential closure of a differential field K is not always minimal over K.

scholarly journals THE MODEL COMPANION OF DIFFERENTIAL FIELDS WITH FREE OPERATORS

2016 ◽  
Vol 81 (2) ◽  
pp. 493-509
Author(s):  
OMAR LEÓN SÁNCHEZ ◽  
RAHIM MOOSA
Keyword(s):  
Mathematical Logic ◽  
Characteristic Zero ◽  
Differential Algebra ◽  
Model Companion ◽  
Finite Algebras ◽  
Closed Fields ◽  
Hensel’S Lemma ◽  
Differential Fields ◽  
Theory Of Fields ◽  
Model Theory Of Fields

AbstractA model companion is shown to exist for the theory of partial differential fields of characteristic zero equipped with free operators that commute with the derivations. The free operators here are those introduced in [R. Moosa and T. Scanlon, Model theory of fields with free operators in characteristic zero, Journal of Mathematical Logic 14(2), 2014]. The proof relies on a new lifting lemma in differential algebra: a differential version of Hensel’s Lemma for local finite algebras over differentially closed fields.

Differentially algebraic group chunks

1990 ◽  
Vol 55 (3) ◽  
pp. 1138-1142 ◽  
Author(s):  
Anand Pillay
Keyword(s):  
Algebraic Group ◽  
Characteristic Zero ◽  
Quantifier Elimination ◽  
Closed Field ◽  
Zariski Topology ◽  
First Order ◽  
Differential Field ◽  
Closed Fields ◽  
Differential Fields ◽  
Algebraically Closed Fields

We point out that a group first order definable in a differentially closed field K of characteristic 0 can be definably equipped with the structure of a differentially algebraic group over K. This is a translation into the framework of differentially closed fields of what is known for groups definable in algebraically closed fields (Weil's theorem).I restrict myself here to showing (Theorem 20) how one can find a large “differentially algebraic group chunk” inside a group defined in a differentially closed field. The rest of the translation (Theorem 21) follows routinely, as in [B].What is, perhaps, of interest is that the proof proceeds at a completely general (soft) model theoretic level, once Facts 1–4 below are known.Fact 1. The theory of differentially closed fields of characteristic 0 is complete and has quantifier elimination in the language of differential fields (+, ·,0,1, −1,d).Fact 2. Affine n-space over a differentially closed field is a Noetherian space when equipped with the differential Zariski topology.Fact 3. If K is a differentially closed field, k ⊆ K a differential field, and a and are in k, then a is in the definable closure of k ◡ iff a ∈ ‹› (where k ‹› denotes the differential field generated by k and).Fact 4. The theory of differentially closed fields of characteristic zero is totally transcendental (in particular, stable).

Model completeness of o-minimal structures expanded by Dedekind cuts

2005 ◽  
Vol 70 (1) ◽  
pp. 29-60 ◽  
Author(s):  
Marcus Tressl
Keyword(s):  
Valuation Ring ◽  
Ordered Set ◽  
Real Closed Field ◽  
Complete Theory ◽  
Closed Field ◽  
Model Completeness ◽  
Unary Predicate ◽  
Minimal Structure ◽  
Totally Ordered Set ◽  
Dedekind Cuts

§1. Introduction. Let M be a totally ordered set. A (Dedekind) cut p of M is a couple (pL, pR) of subsets pL, pR of M such that pL ⋃ pR = M and pL < pR, i.e., a < b for all a ∈ pL, b ∈ pR. In this article we are looking for model completeness results of o-minimal structures M expanded by a set pL for a cut p of M. This means the following. Let M be an o-minimal structure in the language L and suppose M is model complete. Let D be a new unary predicate and let p be a cut of (the underlying ordered set of) M. Then we are looking for a natural, definable expansion of the L(D)-structure (M, pL) which is model complete.The first result in this direction is a theorem of Cherlin and Dickmann (cf. [Ch-Dic]) which says that a real closed field expanded by a convex valuation ring has a model complete theory. This statement translates into the cuts language as follows. If Z is a subset of an ordered set M we write Z+ for the cut p with pR = {a ∈ M ∣ a > Z} and Z− for the cut q with qL = {a ∈ M ∣ a < Z}.

Modeling and dynamics of an ecological-economic model

2019 ◽  
Vol 12 (03) ◽  
pp. 1950030 ◽  
Author(s):  
Wei Liu ◽  
Yaolin Jiang
Keyword(s):  
Economic Model ◽  
Differential Algebra ◽  
Threshold Value ◽  
Formal Series ◽  
Dynamical Analysis ◽  
Positive Equilibrium ◽  
Economic Profit ◽  
Positive Equilibrium Point ◽  
The Stability ◽  
The Impact

In this paper, an eco-economic model with harvesting on biological population is established, which takes the form of a differential-algebra system. The impact of the economic profit from harvesting upon the dynamics of the model is studied. By using a suitable parameterization for the differential-algebra system, we derive an equivalent parameterized system which gives the stability results for the positive equilibrium point of our model. Moreover, based on the parameterized system as well as the approaches of normal form and formal series, the conditions on the Hopf bifurcation and the stability of center are obtained. Several numerical simulations for demonstrating the theoretical results are also presented. Lastly, according to the dynamical analysis, we provide a threshold value for the economic profit, which can maintain the sustainable development of our eco-economic system.

Separably closed fields with higher derivations I

1995 ◽  
Vol 60 (3) ◽  
pp. 898-910 ◽  
Author(s):  
Margit Messmer ◽  
Carol Wood
Keyword(s):  
Quantifier Elimination ◽  
Complete Theory ◽  
Closed Fields

AbstractWe define a complete theory SHFe of separably closed fields of finite invariant e (=degree of imperfection) which carry an infinite stack of Hasse-derivations. We show that SHFe has quantifier elimination and eliminates imaginaries.

scholarly journals Bezout-type theorems for differential fields

2017 ◽  
Vol 153 (4) ◽  
pp. 867-888 ◽  
Author(s):  
Gal Binyamini
Keyword(s):  
Elliptic Curves ◽  
Lattice Points ◽  
Newton Polytope ◽  
Algebraic Varieties ◽  
Number Of Solutions ◽  
Asymptotic Growth ◽  
Closed Fields ◽  
Exponential Bounds ◽  
Differential Fields ◽  
Derivatives Of

We prove analogs of the Bezout and the Bernstein–Kushnirenko–Khovanskii theorems for systems of algebraic differential conditions over differentially closed fields. Namely, given a system of algebraic conditions on the first $l$ derivatives of an $n$-tuple of functions, which admits finitely many solutions, we show that the number of solutions is bounded by an appropriate constant (depending singly-exponentially on $n$ and $l$) times the volume of the Newton polytope of the set of conditions. This improves a doubly-exponential estimate due to Hrushovski and Pillay. We illustrate the application of our estimates in two diophantine contexts: to counting transcendental lattice points on algebraic subvarieties of semi-abelian varieties, following Hrushovski and Pillay; and to counting the number of intersections between isogeny classes of elliptic curves and algebraic varieties, following Freitag and Scanlon. In both cases we obtain bounds which are singly-exponential (improving the known doubly-exponential bounds) and which exhibit the natural asymptotic growth with respect to the degrees of the equations involved.

The independence relation in separably closed fields

1986 ◽  
Vol 51 (3) ◽  
pp. 715-725 ◽  
Author(s):  
G. Srour
Keyword(s):  
Alternative Proof ◽  
Closed Fields ◽  
The Stability ◽  
The One

AbstractWe give an alternative proof of the stability of separably closed fields of fixed Éršov invariant to the one given in [W]. We show that in case the Éršov invariant is finite, the theory is in fact equational. We also characterize the independence relation in those theories.

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