Cofinal extension preserves recursive saturation

1980 ◽  
pp. 338-345 ◽  
Author(s):  
C. Smoryński ◽  
J. Stavi
Keyword(s):  
Recursive Saturation

Nonstandard characterizations of recursive saturation and resplendency

1987 ◽  
Vol 52 (3) ◽  
pp. 842-863 ◽  
Author(s):  
Stuart T. Smith
Keyword(s):  
Peano Arithmetic ◽  
Recursive Saturation ◽  
Recursively Saturated ◽  
Satisfaction Class

AbstractWe prove results about nonstandard formulas in models of Peano arithmetic which complement those of Kotlarski, Krajewski, and Lachlan in [KKL] and [L]. This enables us to characterize both recursive saturation and resplendency in terms of statements about nonstandard sentences. Specifically, a model of PA is recursively saturated iff is nonstandard and -logic is consistent. is resplendent iff is nonstandard, -logic is consistent, and every sentence φ which is consistent in -logic is contained in a full satisfaction class for . Thus, for models of PA, recursive saturation can be expressed by a (standard) -sentence and resplendency by a -sentence.

Jon Barwise and John Schlipf. On recursively saturated models of arithmetic. Model theory and algebra, A memorial tribute to Abraham Robinson, edited by D. H. Saracino and V. B. Weispfenning, Lecture notes in mathematics, vol. 498, Springer-Verlag, Berlin, Heidelberg, and New York, 1975, pp. 42–55. - Patrick Cegielski, Kenneth McAloon, and George Wilmers. Modèles récursivement saturés de l'addition et de la multiplication des entiers naturels. Logic Colloquium '80, Papers intended for the European summer meeting of the Association for Symbolic Logic, edited by D. van Dalen, D. Lascar, and T. J. Smiley, Studies in logic and the foundations of mathematics, vol. 108, North-Holland Publishing Company, Amsterdam, New York, and London, 1982, pp. 57–68. - Julia F. Knight. Theories whose resplendent models are homogeneous. Israel journal of mathematics, vol. 42 (1982), pp. 151–161. - Julia Knight and Mark Nadel. Expansions of models and Turing degrees. The journal of symbolic logic, vol. 47 (1982), pp. 587–604. - Julia Knight and Mark Nadel. Models of arithmetic and closed ideals. The journal of symbolic logic, vol. 47 no. 4 (for 1982, pub. 1983), pp. 833–840. - Henryk Kotlarski. On elementary cuts in models of arithmetic. Fundamenta mathematicae, vol. 115 (1983), pp. 27–31. - H. Kotlarski, S. Krajewski, and A. H. Lachlan. Construction of satisfaction classes for nonstandard models. Canadian mathematical bulletin—Bulletin canadien de mathématiques, vol. 24 (1981), pp. 283–293. - A. H. Lachlan. Full satisfaction classes and recursive saturation. Canadian mathematical bulletin—Bulletin canadien de mathématiques, pp. 295–297. - Leonard Lipshitz and Mark Nadel. The additive structure of models of arithmetic. Proceedings of the American Mathematical Society, vol. 68 (1978), pp. 331–336. - Mark Nadel. On a problem of MacDowell and Specker. The journal of symbolic logic, vol. 45 (1980), pp. 612–622. - C. Smoryński. Back-and-forth inside a recursively saturated model of arithmetic. Logic Colloquium '80, Papers intended for the European summer meeting of the Association for Symbolic Logic, edited by D. van Dalen, D. Lascar, and T. J. Smiley, Studies in logic and the foundations of mathematics, vol. 108, North-Holland Publishing Company, Amsterdam, New York, and London, 1982, pp. 273–278. - C. Smoryński and J. Stavi. Cofinal extension preserves recursive saturation. Model theory of algebra and arithmetic, Proceedings of the Conference on Applications of Logic to Algebra and Arithmetic held at Karpacz, Poland, September 1–7,1979, edited by L. Pacholski, J. Wierzejewski, and A. J. Wilkie, Lecture notes in mathematics, vol. 834, Springer-Verlag, Berlin, Heidelberg, and New York, 1980, pp. 338–345. - George Wilmers. Minimally saturated models. Model theory of algebra and arithmetic, Proceedings of the Conference on Applications of Logic to Algebra and Arithmetic held at Karpacz, Poland, September 1–7, 1979, edited by L. Pacholski, J. Wierzejewski, and A. J. Wilkie, Lecture notes in mathematics, vol. 834, Springer-Verlag, Berlin, Heidelberg, and New York, 1980, pp. 370–380.

1987 ◽  
Vol 52 (1) ◽  
pp. 279-284
Author(s):  
J.-P. Ressayre
Keyword(s):  
New York ◽  
Model Theory ◽  
Foundations Of Mathematics ◽  
Symbolic Logic ◽  
Recursive Saturation ◽  
North Holland Publishing ◽  
Lecture Notes ◽  
Recursively Saturated ◽  
Satisfaction Classes ◽  
Models Of Arithmetic

Models with the ω-property

1989 ◽  
Vol 54 (1) ◽  
pp. 177-189 ◽  
Author(s):  
Roman Kossak
Keyword(s):  
Structural Properties ◽  
Interesting Property ◽  
Order Type ◽  
Countable Model ◽  
The Other ◽  
Recursive Saturation ◽  
Saturated Models ◽  
Other Hand ◽  
To Come ◽  
Recursively Saturated

In [KP] we have studied the problem of determining when a subset of a (countable) model M of PA can be coded in an elementary end extension of M. Sets with this property are called elementary extensional. In particular we can ask whether there are elementary extensional subsets of a model which have order type ω. It turns out that having elementary extensional subsets of order type ω is an interesting property connected with other structural properties of models of PA. We will call this property the ω-property. In [KP] the problem of characterizing models with the ω-property was left open. It is still open, and the aim of this paper is to present a collection of results pertaining to it. It should be mentioned that the same notion was studied by Kaufmann and Schmerl in [KS2] in connection with some weak notions of saturation which they discuss there. Our notion of a model with the ω-property corresponds to the notion of an upward monotonically ω-lofty cut.It is fairly easy to see that countable recursively saturated models (or in fact all recursively saturated models with cofinality ω) and all short recursively saturated models have the ω-property (Proposition 1.2 below). On the other hand, if we had asked the question about the existence of models with the ω-property before 1975 (when recursively saturated models were introduced) the answer would probably not have been that easy and we would have to come to notions close to recursive saturation.

Nonstandard Characterizations of Recursive Saturation and Resplendency

1987 ◽  
Vol 52 (3) ◽  
pp. 842 ◽  
Author(s):  
Stuart T. Smith
Keyword(s):  
Recursive Saturation

Toward model theory through recursive saturation

1978 ◽  
Vol 43 (2) ◽  
pp. 183-206 ◽  
Author(s):  
John Stewart Schlipf
Keyword(s):  
Set Theory ◽  
Model Theory ◽  
Traditional Model ◽  
Recursive Saturation ◽  
Admissible Sets ◽  
Saturated Models ◽  
Skolem Theorem ◽  
Local Results ◽  
Recursively Saturated ◽  
By Products

One of the most significant by-products of the study of admissible sets with urelements is the emphasis it has given to recursively saturated models. As suggested in [Schlipf, 1977], countable recursively saturated models (for finite languages) possess many of the desirable properties of saturated and special models. The notion of resplendency was introduced to isolate some of these desirable properties. In §§1 and 2 of this paper we study these parallels, showing how they can be exploited to give new proofs of some traditional model theoretic theorems. This yields both pedagogical and philosophical advantages: pedagogical since countable recursively saturated models are easier to build and manipulate than saturated and special models; philosophical since it shows that uncountable models — which the downward Lowenheim–Skolem theorem tells us are in some sense not basic in the study of countable theories — are not needed in model theoretic proofs of these theorems. In §3 we apply our local results to get results about resplendent models of ZF set theory and PA (Peano arithmetic). In §4 we shall examine certain analogous results for admissible languages, most similar to, and seemingly generally slightly weaker than, already known results. (The Chang–Makkai sort of result, however, is new.)Although this paper is an outgrowth of work with admissible sets with urelements, I have tried to keep it as accessible as possible to those with a background only in finitary model theory. Thus §§1,2, and 3 should not involve any work with admissible sets. §4, however, is concerned with some admissible analogues to results in §2 and necessarily uses certain technical results of §11 5 of [Schlipf, 1977].

Game sentences, recursive saturation and definability

1980 ◽  
Vol 45 (1) ◽  
pp. 35-46
Author(s):  
Victor Harnik
Keyword(s):  
Recursive Saturation ◽  
The Past ◽  
Recursively Saturated

In the past 10 years much progress occurred in the direction of unifying the treatment of finitary Lωω and infinitary logic. We have especially in mind the study of countable admissible fragments (of which Lωω is a particular case) initiated by Barwise in [1] (cf. also [2]), the introduction of -recursively saturated structures by Ressayre in [22] (for these were independently introduced in [3]) and game sentences as studied by Vaught in [26] (see also Svenonius [25] and Moschovakis [19], [20]). A good reference for these topics is [17].In this paper we illustrate the use of these tools for deducing definability theorems. We go beyond the known results as seen from the discussion that follows.Let L be a language and P a (say, unary) additional predicate. Consider a sentence σ(P) in the language L(P). There are two types of definability theorems: the “Beth type” and the “Svenonius type”. Beth's theorem [4] characterizes the condition:(i)′ for any ;while Svenonius' result [24] characterizes:(i)″ for any , every L-automorphism of is an L(P)-automorphism.

A certain class of models of Peano arithmetic

1983 ◽  
Vol 48 (2) ◽  
pp. 311-320 ◽  
Author(s):  
Roman Kossak
Keyword(s):  
Peano Arithmetic ◽  
Recursive Saturation ◽  
Saturated Models ◽  
The Subject ◽  
Recursively Saturated ◽  
Satisfaction Classes ◽  
The Way

This paper is devoted to the study of recursively and short recursively saturated models of PA by means of so-called nonstandard satisfaction methods. The paper is intended to be self-contained. In particular, no knowledge of nonstandard satisfaction classes is assumed. In fact we shall not use this notion explicitly.We define a certain property of models of PA which we call the S-property and prove that properly short recursively saturated models (see Definition 2.1. below) are exactly short models with the S-property. The main result is that all properly short recursively saturated models are elementary cuts of recursively saturated models. This is a generalization to the uncountable case of the theorem of C. Smorynski [9] and is an easy application of some general results concerning cofinal extensions of models of PA which we discuss in §3.On the way we obtain another proof of the result of Smorynski and Stavi [10] which says that short recursive and recursive saturation is preserved under cofinal extensions.The author wants to thank H. Kotlarski and W. Marek for valuable suggestions concerning the subject of the paper.Special thanks must also go to J. Paris for the lemma used in the proof of Theorem 3.5.

Indicators, recursive saturation and expandability

1981 ◽  
Vol 114 (2) ◽  
pp. 127-139 ◽  
Author(s):  
L. Kirby ◽  
K. McAllon ◽  
R. Murawski
Keyword(s):  
Recursive Saturation

Additive structure in uncountable models for a fixed completion of P

1983 ◽  
Vol 48 (3) ◽  
pp. 623-628 ◽  
Author(s):  
Julia F. Knight
Keyword(s):  
Standard System ◽  
Saturated Model ◽  
Additive Structure ◽  
Recursive Saturation ◽  
Nonstandard Model ◽  
Recursively Saturated ◽  
Recursively Saturated Model

In [6], Nadel showed that if is a recursively saturated model of Pr = Th(ω, +) of power at most ℵ1, then there is a model such that ≡ ∞ω and can be expanded to a recursively saturated model of P. For a fixed completion T of P, can be chosen to have a recursively saturated expansion to a model of T just in case is recursive in T-saturated. (“Recursive in T-saturation” is defined just like recursive saturation except that the sets of formulas considered are those that are recursive in T.)Nadel also showed in [6] that for a fixed completion T of P, a countable nonstandard model of Pr can be expanded to a model of T (not necessarily recursively saturated) iff satisfies a condition called “exp(T)-saturation.” This condition is stronger than recursive saturation but weaker than recursive in T-saturation. Nadel left open the problem of characterizing the models of Pr of power ℵ1 such that for some , ≣ ∞ω and can be expanded to a model of T. The present paper gives such a characterization. The condition on is that it is recursively saturated, and for each n ∈ ω, the set Tn of Πn-sentences of T is recursive in some type realized in .This result can be interpreted in various ways, just as the results from [6] were interpreted in various ways in [4]. Friedman [2] introduced the notion of a “standard system.”

Models of arithmetic and closed ideals

1982 ◽  
Vol 47 (4) ◽  
pp. 833-840 ◽  
Author(s):  
Julia Knight ◽  
Mark Nadel
Keyword(s):  
Closed Ideal ◽  
Turing Degrees ◽  
Saturated Model ◽  
Recursive Saturation ◽  
New Information ◽  
Recursively Saturated ◽  
Recursively Saturated Model ◽  
Saturated Structure ◽  
Models Of Arithmetic ◽  
Natural Way

A set J of Turing degrees is called an ideal if (1) J ≠ ∅, (2) for any pair of degrees ã, , if ã, ϵ J, then ã ⋃ ϵJ, and (3) for any ⋃ ϵ J and any , if < ⋃, then ϵ J. A set J of degrees is said to be closed if for any theory T with a set of axioms of degree in J, T has a completion of degree in J.Closed ideals of degrees arise naturally in the following way. If is a recursively saturated structure, let I() = { for some ā ϵ }. Let D() = {: is recursive in d-saturated}. (Recursive in d-saturation is defined like recursive saturation except that the sets of formulas considered are recursive in d.) These two sets of degrees were investigated in [2]. It was shown that if is a recursively saturated model of P, Pr = Th(ω, +), or Pr′ = Th(Z, +, 1), then I() = D(), and this set is a closed ideal. Any closed ideal J can be represented as I() = D() for some recursively saturated model of Pr′. For sets J of power at most ℵ1, Pr′ can be replaced by P.Assuming CH, all closed ideals have power at most ℵ1, but if CH fails, there are closed ideals of power greater than ℵ1, and it is not known whether these can be represented as I() = D() for a recursively saturated model of P.In the present paper, it will first be shown that information about representation of closed ideals provides new information about an old problem of MacDowell and Specker [6] and extends an old result of Scott [8] in a natural way. It will also be shown that the representation results from [2] answer a problem of Friedman [1]. This part of the paper is aimed at convincing the reader that representation problems are worth investigating.

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