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first-order and higher-order logic, model theory, set theory, proof theory, computability theory, formal languages, definability, interplay of syntax and semantics, constructive logic, intuitionism, philosophical logic, modal logic, completeness, Gödel incompleteness, decidability, undecidability, theories of truth, truth revision, consistency.

45 votes
6 answers
8k views

Situation with Artemov's paper?

Artemov's paper on Goedel's theorem has been on the arxiv since 2019. There was a (less than fully friendly) discussion of this on FoM. At stackexchange, I found only a brief mention at this MSE pos …
Mikhail Katz's user avatar
  • 16.6k
38 votes
6 answers
3k views

What are the advantages of the more abstract approaches to nonstandard analysis?

This question does not concern the comparative merits of standard (SA) and nonstandard (NSA) analysis but rather a comparison of different approaches to NSA. What are the concrete advantages of the ab …
Mikhail Katz's user avatar
  • 16.6k
35 votes
9 answers
14k views

What is... a grossone?

Y. Sergeyev developed a positional system for representing infinite numbers using a basic unit called a "grossone", as well as what he calls an "infinity computer". The mathematical value of this see …
Mikhail Katz's user avatar
  • 16.6k
22 votes
2 answers
2k views

Euler's mathematics in terms of modern theories?

Some aspects of Euler's work were formalized in terms of modern infinitesimal theories by Laugwitz, McKinzie, Tuckey, and others. Referring to the latter, G. Ferraro claims that "one can see in operat …
Mikhail Katz's user avatar
  • 16.6k
21 votes
9 answers
5k views

Was the early calculus inconsistent?

This question does NOT concern the RIGOR, or lack thereof, of the early calculus. Rather the question is of its CONSISTENCY. George Berkeley wrote in 1734 with reference to the early calculus that s …
Mikhail Katz's user avatar
  • 16.6k
18 votes
2 answers
1k views

New articles by Errett Bishop on constructive type theory?

Recently two formerly unknown articles by Errett Bishop (1928-1983) were posted online by Martín Escardó. One is entitled "A general language", deals with constructive type theory, and is 28 pages lon …
Mikhail Katz's user avatar
  • 16.6k
17 votes
1 answer
2k views

What is the precise relationship between o-minimal theory and Grothendieck's "Esquisse d'un ...

I have seen various references in the literature to such a connection but they tend to assume that the reader is familiar with the connection, and limit themselves to providing additional detail. So …
Mikhail Katz's user avatar
  • 16.6k
15 votes
1 answer
807 views

Are key theorems finitistically reducible?

Simpson writes on page 378 of his Subsystems of Second Order Arithmetic: "For example, all of the following key theorems of infinitistic mathematics are provable in WKL$_0$ and therefore, by theorem I …
Mikhail Katz's user avatar
  • 16.6k
13 votes
6 answers
2k views

Intuitionistic logic as quantization of classical logic?

A classically trained mathematician is more likely to be familiar (at least anecdotally) with an area of mathematical physics such as deformation quantization than with intuitionistic logic. It is he …
Mikhail Katz's user avatar
  • 16.6k
8 votes
0 answers
1k views

What's Reeb's take on naive integers?

Georges Reeb's "claim Q" is the statement that "naive integers don't fill up $\mathbb{N}$". To anyone familiar with model theory this could easily be interpreted as the existence of nonstandard models …
Mikhail Katz's user avatar
  • 16.6k
8 votes
1 answer
586 views

Con(PA) via non-well-foundedness?

Lumsdaine made the following interesting comment: if Con(PA) fails in a non-standard model, it means it contains a “proof of non-standard length” of a contradiction from PA. With a little work, one …
Mikhail Katz's user avatar
  • 16.6k
7 votes
2 answers
1k views

Salvaging Leibnizian formalism?

Can one justify Leibniz's formalism in a suitable algebraic or topological context? We have published some papers recently where we argue that Leibniz's formalism for the calculus wasn't inconsisten …
Mikhail Katz's user avatar
  • 16.6k
7 votes
4 answers
541 views

A conservative extension of Peano Arithmetic

Ulrich Kohlenbach makes the following intriguing comment here: "In the 70s S. Feferman introduced a mathematically strong system S=restricted(PA^omega)+QF-AC+mu for classical mathematics (and in part …
Mikhail Katz's user avatar
  • 16.6k
7 votes
6 answers
3k views

Looking for a source for Intended Interpretation

Hao Wang writes: "The originally intended, or standard, interpretation takes the ordinary nonnegative integers $\{0, 1, 2, \ldots \}$ as the domain, the symbols $0$ and $1$ as denoting zero and one, a …
Mikhail Katz's user avatar
  • 16.6k
6 votes
5 answers
2k views

Standard models of N and R: An Alice/Bob approach

This is a question about a comment in a recent publication by Roman Kossak. Kossak wrote: "Nonstandardness in set theory has a different nature. In arithmetic, there is one intended object of study …
Mikhail Katz's user avatar
  • 16.6k

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