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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.

7 votes
2 answers
1k views

candidate for rigorous _mathematical_ definition of "canonical"?

In this question: What is the definition of "canonical"? , people gave interesting "philosophical" takes on what the word "canonical" means. Moreover I percieved an underlying opinion that there was n …
Kevin Buzzard's user avatar
59 votes
8 answers
8k views

Cauchy reals and Dedekind reals satisfy "the same mathematical theorems"

The succinct question The conjecture of Birch and Swinnerton-Dyer (to take a random example) mentions L-functions and hence the complex numbers and hence the real numbers (because the complexes are b …
Kevin Buzzard's user avatar
21 votes

When are two proofs of the same theorem really different proofs

My opinion, and it's only an opinion, is that it would be very difficult to formalise what it means for two proofs to be different. Here's an intuitive reason why. If I give you two proofs of theorem …
Kevin Buzzard's user avatar
54 votes
2 answers
5k views

Automatically solving olympiad geometry problems

Warning: I am only an amateur in the foundations of mathematics. My understanding of this Wikipedia page about Tarski's axiomatization of plane geometry (and especially the discussion about decidabil …
Kevin Buzzard's user avatar
37 votes

Does anyone still seriously doubt the consistency of $ZFC$?

For decades I was not particularly suspicious about the consistency of ZFC but I was rather surprised about how it had become the standard choice when it contained axioms such as Replacement, which se …
37 votes
Accepted

Is "all categorical reasoning formally contradictory"?

Note: I am not a historian. I'm just guessing as to what prompted the comments. Here's my guess: if you do set theory naively, in the old-fashioned "anything is a set" way, then you run into Russell' …
Kevin Buzzard's user avatar
5 votes

Textbook recommendations for undergraduate proof-writing class

I am not so sure of the US system but one of the books we recommend at our university is Martin Liebeck's "A concise introduction to pure mathematics". http://www.amazon.co.uk/Concise-Introduction-Pu …
31 votes

Most 'unintuitive' application of the Axiom of Choice?

The fact that there exist non-measurable sets is highly counter-intuitive; the reason we don't find it so is that we've all been conditioned from day 1 to do measure theory very carefully, and define …