Georg Kreisel. Some concepts concerning formal systems of number theory. Mathematische Zeitschrift, vol. 57 no. 1 (1952), pp. 1–12.

1966 ◽  
Vol 31 (1) ◽  
pp. 128-128
Author(s):  
Gert H. Müller
Keyword(s):  

1957 ◽  
Vol 22 (1) ◽  
pp. 1-14 ◽  
Author(s):  
Leon Henkin

The concepts of ω-consistency and ω-completeness are closely related. The former concept has been generalized to notions of Γ-consistency and strong Γ-consistency, which are applicable not only to formal systems of number theory, but to all functional calculi containing individual constants; and in this general setting the semantical significance of these concepts has been studied. In the present work we carry out an analogous generalization for the concept of ω-completeness.Suppose, then, that F is an applied functional calculus, and that Γ is a non-empty set of individual constants of F. We say that F is Γ-complete if, whenever B(x) is a formula (containing the single free individual variable x) such that ⊦ B(α) for every α in Γ, then also ⊦ (x)B(x). In the paper “Γ-con” a sequence of increasingly strong concepts, Γ-consistency, n = 1,2, 3,…, was introduced; and it is possible in a formal way to define corresponding concepts of Γn-completeness, as follows. We say that F is Γn-complete if, whenever B(x1,…, xn) is a formula (containing exactly n distinct free variables, namely x1…, xn) such that ⊦ B(α1,…,αn) for all α1,…,αn in Γ, then also ⊦ (X1)…(xn)B(x1,…,xn). However, unlike the situation encountered in the paper “Γ-con”, these definitions are not of interest – for the simple reason that F is Γn-complete if and only if it is Γ-complete, as one easily sees.



1962 ◽  
Vol 27 (1) ◽  
pp. 11-18 ◽  
Author(s):  
S. C. Kleene

Let Pp, Pd, and N be the intuitionistic formal systems of prepositional calculus, predicate calculus, and elementary number theory, respectively.1 Consider the following six propositions.8(1) ├A V B only if ├A or ├B.(2) ├∋xA(x) only if ├Ã(t) for some formula Ã(x) congruent to A(x) and some term t free for x in Ã(x).



1952 ◽  
Vol 57 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Georg Kreisel
Keyword(s):  


1991 ◽  
Vol 56 (1) ◽  
pp. 1-49 ◽  
Author(s):  
Solomon Feferman

To what extent can mathematical thought be analyzed in formal terms? Gödel's theorems show the inadequacy of single formal systems for this purpose, except in relatively restricted parts of mathematics. However at the same time they point to the possibility of systematically generating larger and larger systems whose acceptability is implicit in acceptance of the starting theory. The engines for that purpose are what have come to be called reflection principles. These may be iterated into the constructive transfinite, leading to what are called recursive progressions of theories. A number of informative technical results have been obtained about such progressions (cf. Feferman [1962], [1964], [1968] and Kreisel [1958], [1970]). However, for some years I had hoped to give a more realistic and perspicuous finite generation procedure. This was first done in a rather special way in Feferman [1979] for the characterization of predicativity, which may be regarded as that part of mathematical thought implicit in our acceptance of elementary number theory. What is presented here is a new and simple notion of the reflective closure of a schematic theory which can be applied quite generally.Two examples of schematic theories in the sense used here are versions of Peano arithmetic and Zermelo set theory.



1978 ◽  
Vol 43 (2) ◽  
pp. 228-246 ◽  
Author(s):  
Michael Beeson

This paper is devoted to the general question, which assertions φ have the property,if φ is provable classically, then φ is(*) provable constructively.More generally, we consider the question, what is the “constructive content” of a given classical proof? Our aim is to formulate rules in a form applicable to mathematical practice. Often a mathematician has the feeling that there will be no difficulty constructivizing a certain proof, only a number of routine details; although it can be quite laborious to set them all out. We believe that most such situations will come quite easily under the scope of the rules given here; the metamathematical machinery will then take care of the details.This basic idea is not new; it has been discussed by Gödel and by Kreisel. Kreisel's investigations [Kr] were based on Herbrand's theorem; in unpublished memoranda he has also used Gödel's methods on some examples. These methods of Gödel (the double-negation and Dialectica interpretations) lie at the root of our work here. Previous work, however, has been limited to traditional formal systems of number theory and analysis. It is only recently that formal systems adequate to formalize constructive mathematics as a whole have been developed. Thus, for the first time we are in a position to formulate logical theorems which are easily applicable to mathematical practice. It is this program which we here carry out.Now that the work has been placed in some historical context, let us return to the main question: which φ have the property (*)? Upon first considering the problem, one might guess that any φ which makes no existential assertions (including disjunctions) should have the property (*).



1960 ◽  
Vol 25 (1) ◽  
pp. 27-32 ◽  
Author(s):  
Ronald Harrop

In a previous paper [1] it was proved, among other results, that a closed disjunction of intuitionistic elementary number theory N can be proved if and only if at least one of its disjunctands is provable and that a closed formula of the type (Ex)B(x) is provable in N if and only if B(n) is provable for some numeral n. The method of proof was to show that, as far as closed formulas are concerned, N is equivalent to a calculus N1 for which the result is immediate. The main step in the proof consisted in showing that the set of provable formulas of N1 is closed under modus ponens. This was done by obtaining a subset of the set which is closed under modus ponens and contains all members of the original set, with which it is therefore identical.



Author(s):  
Hugh L. Montgomery ◽  
Robert C. Vaughan
Keyword(s):  


Author(s):  
R. P. Burn
Keyword(s):  


Author(s):  
J. H. Loxton
Keyword(s):  




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