Article contents
Arithmetic and the theory of types
Published online by Cambridge University Press: 12 March 2014
Extract
A hundred years ago, Frege proposed a logical definition of the natural numbers based on the following idea:
He replaced this circular definition by the following one:
He tried afterwards to found his theory over a notion of class satisfying a general comprehension principle:
Russell quickly derived a contradiction from this principle (the famous Russell's paradox) but saved Frege's arithmetic with his theory of types based on the following comprehension principle:
In 1979, talking at the Claude Bernard University in Lyon, I remarked that 3 types suffice to provide Frege's arithmetic, showing in fact that PA2 (second order Peano arithmetic) holds in TT3 + AI (theory of types 0, 1, 2 plus a suitable axiom of infinity). I asked whether TT3 + AI was a conservative extension of PA2. Pabion [3] gave a positive answer by a subtle use of the Fraenkel-Moskowski method. This result will be improved in the present paper, with a view to getting models of NF3 + AI in which Frege's arithmetic forms a model isomorphic to a given countable model of PA2.
- Type
- Research Article
- Information
- Copyright
- Copyright © Association for Symbolic Logic 1984
References
REFERENCES
- 2
- Cited by