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Gödel's Second incompleteness theorem for Q

Published online by Cambridge University Press:  12 March 2014

A. Bezboruah  and
J. C. Shepherdson
A. Bezboruah
Affiliation:
Gauhati University, Oauhati 781014, Assam, India
J. C. Shepherdson
Affiliation:
Bristol University, Bristol BS8 1TW, England
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Extract

For the first Gödel incompleteness theorem, the existence in a formal system of arithmetic L of a sentence which is neither provable nor refutable, all that is required of the formula Th(x) of L used to express the notion ‘x is the g.n. (gödel number) of a theorem of L’ is mere numeralwise correctness, i.e. that for a numeral n, Th(n) is provable in L iff n is the g.n. of a theorem of L. It is well known that much more is needed for the second Gödel incompleteness theorem, the unprovability in L of the formula Con =df ¬(∃y, z)(Th(y) ∧ Th(z) ∧ neg(z, y)), which (if neg expresses negation) expresses the consistency of L. Conditions sufficient for this second theorem, more or less as stated by Hilbert-Bernays [1, p. 286] and elegantly formulated by Löb [2] may with a cavalier disregard for the distinction between use and mention be stated thus: The result of the first incompleteness theorem: there is a sentence G such that ⊢G ↔ ¬Th G), together with, if ⊢A then ⊢Th A, if ⊢(A → B) then ⊢(Th A → Th B), ⊢(Th A → Th Th A). On the other hand Feferman [3], Kreisel [4, p. 154] and Jeroslow [9] have given examples of systems and consistency formulae, based on numeralwise correct formulae Th(x), which are provable within the system.

Type
Research Article
Information
The Journal of Symbolic Logic , Volume 41 , Issue 2 , June 1976 , pp. 503 - 512
Copyright
Copyright © Association for Symbolic Logic 1976

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References

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