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1 vote
0 answers
122 views

How could I formally express: System F cannot express universal quantification over things that are not types? [closed]

I'm trying to understand exactly why it is that https://ncatlab.org/nlab/show/computational+trilogy states that quantification requires dependent types, and why this wouldn't be possible to achieve ...
shintuku's user avatar
  • 113
6 votes
1 answer
273 views

Consistency in pure type systems

Summary My question is about how (i) a certain presentation of pure type systems in the $\lambda$-cube, bears on (ii) a standard definition of consistency in pure type systems. In short, I'm ...
Spaceka13's user avatar
7 votes
1 answer
375 views

Criterion for the consistency of pure type systems

Pure type systems are characterized in an almost combinatorial way: a set of axioms $\star_i : \star_j$, and a set of triples $(\star_i, \star_j, \star_k)$ saying when the dependent product $\prod_{x :...
Trebor's user avatar
  • 1,262
1 vote
0 answers
219 views

What is the proof theoretic strength of PCF?

Godel's system $T$ means different, although equivalent, things to different people. To people working in the traditon of mathematical logic, $T$ is a quantifier-free equational theory of arithmetic ...
Not_Here's user avatar
  • 482
12 votes
2 answers
3k views

How can the simply typed lambda calculus be Turing-incomplete, yet stronger than second-order logic?

It is well-known that the simply typed lambda calculus is strongly normalizing (for instance, Wikipedia). Hence, it is not strong enough to be Turing-complete, as also mentioned on the Wikipedia page ...
Mike Battaglia's user avatar
11 votes
3 answers
1k views

How to handle sums in Tait's reducibility proof of strong normalisation?

I've been reading Girard et al's 'Proofs and Types', which in Chapter 6 presents a proof of strong normalisation for the simply typed lambda calculus with products and base types. The proof is based ...
RAC's user avatar
  • 113