1982
DOI: 10.2307/2273386
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On the consistency of an impredicative subsystem of Quine's NF

Abstract: NFP is the predicative fragment of NF. In this system we do not allow a set to exist if it cannot be defined without using quantifiers ranging over its type or parameters of a higher type. NFI is a less restrictive fragment located between NFP and NF.We show that NFP is really weaker than NFI; similarly, NFI is weaker than NF. This result will be obtained in the following manner: on the one hand, we will show that NFP can be proved consistent in elementary arithmetic and that second order arithmetic is interpr… Show more

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Cited by 20 publications
(24 citation statements)
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“…As usual for Quine's systems, we need stratification ; we also define a restricted notion thereof, which is motivated by the consideration of “loosely predicative” class existence axioms (cf. [3, Definition 1.1, p. 131]).…”
Section: Background On Sans-serifnfmentioning
confidence: 99%
See 1 more Smart Citation
“…As usual for Quine's systems, we need stratification ; we also define a restricted notion thereof, which is motivated by the consideration of “loosely predicative” class existence axioms (cf. [3, Definition 1.1, p. 131]).…”
Section: Background On Sans-serifnfmentioning
confidence: 99%
“…By a theorem of Crabbé, sans-serifNFI is provably consistent, say, in third order arithmetic (at most) [3, p. 134, Theorem 1]. The details of the (different) consistency proofs for sans-serifNFI can be found in [3] and in [8, Theorem 3, p. 187].…”
Section: Background On Sans-serifnfmentioning
confidence: 99%
“…Remark 3 By a theorem of Crabbè 1982, NFI is provably consistent in third order arithmetic. The details of the (different) consistency proofs for NFI can be found in Crabbè 1982 andHolmes 1995. In order to carry out a Kripke-like construction in the NF-systems and to represent the syntax, we shall essentially exploit Quine's homogeneous pairing operation, which does require extensionality and the existence of a copy of the natural numbers.…”
Section: Other Systemsmentioning
confidence: 99%
“…In fact, it is even inconsistent with one of the other known consistent fragments of NF (predicative NF , described in [4]). We do not expand on this here.…”
Section: Inhomogeneity Of Urelementsmentioning
confidence: 99%