An arithmetical interpretation of dynamic propositional logic (DPL) is a mapping ƒ satisfying the following: (1) ƒ associates with each formula A of DPL a sentence ƒ(A) of Peano arithmetic (PA) and with each program α a formula ƒ(α) of PA with one free variable describing formally a supertheory of PA; (2) ƒ commutes with logical connectives; (3) ƒ([α]A) is the sentence saying that ƒ(A) is provable in the theory ƒ(α); (4) for each axiom A of DPL, ƒ(A) is provable in PA (and consequently, for each A provable in DPL, ƒ(A) is provable in PA). The arithmetical completeness theorem is proved saying that a formula A of DPL is provable in DPL iff for each arithmetical interpretation ƒ, ƒ(A) is provable in PA. Various modifications of this result are considered.

Let I be a countable jump ideal in = 〈The Turing degrees, ≤〉. The central theorem of this paper is:

a is a uniform upper bound on I iff a computes the join of an I-exact pair whose double jump a(1) computes.

We may replace “the join of an I-exact pair” in the above theorem by “a weak uniform upper bound on I”.

We also answer two minimality questions: the class of uniform upper bounds on I never has a minimal member; if ⋃I = Lα[A] ⋂ ωω for α admissible or a limit of admissibles, the same holds for nice uniform upper bounds.

The central technique used in proving these theorems consists in this: by trial and error construct a generic sequence approximating the desired object; simultaneously settle definitely on finite pieces of that object; make sure that the guessing settles down to the object determined by the limit of these finite pieces.

Quine has given a method for eliminating the bound variables in first-order predicate logic establishing thus a variable-free formulation called predicate-functor logic. The purpose of this paper is to give an autonomous and complete proof procedure for Quine's predicate-functor logic with identity, without presupposing axioms or inference rules for quantification theory or, for that matter, any other logic.

In this paper T will always be a countable ℵ0-stable theory, and in this introduction a model of T will mean a countable model.

One of the main notions we introduce is that of almost homogeneous model: we say that a model M of T is almost homogeneous if for all ā and finite sequences of elements in M, if the strong type of ā is the same as the strong type of (i.e. for all equivalence relations E, definable over the empty set and with a finite number of equivalence classes, ā and are in the same equivalence class), then there is an automorphism of M taking ā to . Although this is a weaker notion than homogeneity, these models have strong properties, and it can be seen easily that the Scott formula of any almost homogeneous model is in L1. In fact, Pillay [Pi.] has shown that almost homogeneous models are characterized by the set of types they realize.

The motivation of this research is to distinguish two classes of ℵ0-Stable theories:

(1) theories such that all models are almost homogeneous;

(2) theories with 2ℵ0 nonalmost homogeneous models.

The example of theories with Skolem functions [L. 1] (almost homogeneous is then equivalent to homogeneous) seems to indicate a link between these properties and the notion of multidimensionality, and that nonmultidimensional theories are in the first case.

In [5], Kleene extended previous notions of computations to objects of higher finite type in the maximal type-structure of functionals given by:

Tp(0) = N = the natural numbers,

Tp(n + 1) = NTp(n) = the set of total maps from Tp(n) to N.

He gave nine schemata, S1–S9, for describing algorithms for computations from a finite list of functionals, and indices to denote these algorithms. It is generally agreed that S1-S9 give a natural concept of computations in higher types.

The type-structure of countable functions, Ct(n) for n ϵ N, was first developed by Kleene [6] and Kreisel [7]. It arises from the notions of ‘constructivity’, and has been extensively studied as a domain for higher type recursion theory. Each countable functional is globally described by a countable amount of information coded in its associate, and it is determined locally by a finite amount of information about its argument. The countable functionals are well summarised in Normann [9], and treated in detail in Normann [8].

The purpose of this paper is to discuss a generalisation of the countable functionals, which we shall call the countably based functions, Cb(n) for n ϵ N. It is suggested by the notions of ‘predicativity’, in which we view N as a completed totality, and build higher types on it in a constructive manner. So we shall allow quantification over N and include application of 2E in our schemata. Each functional is determined locally by a countable amount of information about its argument, and so is globally described by a continuum of information coded in its associate, which will now be a type-2 object. This generalisation, obtained via associates, was proposed by Wainer, and seems to reflect topological properties of the countable functionals.

In this paper we consider the special case of the Banach-Mazur game played on a topological space when the space also has an underlying Boolean Algebra structure. This case was first studied by Jech [2]. The version of the Banach-Mazur game we will play is the following game played on the Boolean algebra:

Players I and II alternate moves playing a descending sequence of elements of a Boolean algebra ℬ.

Player II wins the game iff Πi∈ωbi ≠ 0. Jech first considered these games and showed:

Theorem (Jech [2]). ℬ is (ω1, ∞)-distributive iff player I does not have a winning strategy in the game played on ℬ.

If ℬ has a dense ω-closed subset then it is easy to see that player II has a winning strategy in this game. This paper establishes a partial converse to this, namely it gives cardinality conditions on ℬ under which II having a winning strategy implies ω-closure.

In the course of proving the converse, we consider games of length > ω and generalize Jech's theorem to these games. Finally we present an example due to C. Gray that stands in counterpoint to the theorems in this paper.

In this section we give a few basis definitions and explain our notation. These definitions are all standard.

The quantifier Qm,n binds m + n variables. In the κ-interpretation M ⊨ means that there is a κ-powered proper subset X of ∣M∣ such that whenever ā ∈ mX and then M ⊨ ϕā, . If σ ∈ Lm, n has a model in the κ-interpretation does it have a model in the λ-interpretation? For σ ∈ L1, 1, κ regular and uncountable, and λ = ω1 the answer is yes.

T.K. Menas [4, pp. 225–234] introduced a combinatorial property Χ(μ) of a measure μ on a supercompact cardinal κ and proved that measures with this property also have the partition property. We prove here that Menas' property is not equivalent to the partition property. We also show that if a is the least cardinal greater than κ such that Pκα bears a measure without the partition property, then α is inaccessible and -indescribable.

In Forcing and reducibilities, I [20] we reviewed various forcing techniques in the context of arithmetic. This second part deals with the same topics in the context of analysis. The numbering of sections is the continuation of the numbering of the first part. For the reader's convenience, we collect in an independent bibliography the papers which are referred to in this part.

La communauté mathématique doit être reconnaissante à Saharon Shelah pour une invention d'une ingénieuse simplicité, celle d'avoir associé à chaque structure M une structure Meq comprenant, outre les éléments de M, des “éléments imaginaires” qui sont virtuellement présents dans M. La finalité de cette construction est de pourvoir toute formule à paramètres dans M, et même dans Meq, d'un ensemble de définition minimum; tout cela est rappelé dans la première section du présent article.

On peut a priori douter de l'utilité d'une construction si innocente, dont la propriété fondamentale est pratiquement évidente; et pourtant elle a été abondamment montrée par son auteur, à qui elle a permis, dans les théorèmes de classification des modèles, une décomposition des types en éléments simples, qu'on ne voit pas dans M.

Cette construction d'un plus petit ensemble de définition pour une formule en rappelle une autre, qui est bien connue des algébristes, celle du corps de définition d'un idéal. Et comme la théorie des corps algébriquement clos de caractéristique donnée élimine les quanteurs, on a le sentiment que l'adjonction d'imaginaires aux modèles de cette théorie est inutile, en un mot qu'elle “élimine les imaginaires”; pour vérifier le bien-fondé de ce sentiment, il convient d'abord de préciser ce qu'on entend par là, ce qui est fait dans la deuxième section.

In spite of the philosophical significance of higher-order modal logic, the modal logician's main concern has been with sentential logic. In this paper we do not intend to go into philosophical details, but we only remark that higher-order modal logic has a close relationship with Montague's well-known idea of “universal grammar”, which is an ambitious attempt to build a logical theory of natural languages with exact syntax and semantics, comparable with the artificial languages of mathematical logic. For this matter, the reader can consult, e.g., Montague [8], [9] and Gallin [2].

The Cantor-Bendixson theorem says: For every closed set , ∣∣ ≤ ω0 ∨ ⊇ perfect (and therefore is countable or has the power of the continuum). W. H. Young proved the alternative for Gδ-sets, and Hausdorff extended it to Souslin-sets. Cantor used his ordinals to prove the theorem (I like to think he invented them for this purpose). In Hausdorff's Mengenlehre ordinals do not officially enter in either of the three proofs. You should try to put them back. It is very important never to hide away ω1 when it actually is there, and it is there when the continuum problem is the subject.

In Davis [6] you find that Cantor's alternative is equivalent to another alternative: (I wins ) ∨ (J wins ). Here means a lopsided game in which one of the players makes long moves on the game tree. So, the classical theorems can be restated as determinacy results for lopsided games, and now I make this observation: The original CB-proof “actually presents” a winning strategy. The HD-proofs do no such thing; all you know at the end is existence of a winning strategy (and Davis' remark is needed to gain this knowledge).

You understand now why I like CB-proofs, particularly for determinacy of games. They do exist also for games in which both players make short moves. Many years ago I tried to publish such a proof for determinacy of Fσ-games. The referee said it was not worth the trouble. I say you should remake this proof (it is a special case of the one presented in this paper), because it is the ideal of a determinacy proof.

We find necessary and sufficient conditions for compatibility of the Myhill and the Nerode extensions of a combinatorial function to the isols.