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History and philosophy of mathematics, biographies of mathematicians, mathematics education, recreational mathematics, communication of mathematics.

3 votes

First known proof of $\sqrt 2$ is irrational with prime factorization?

Here is a proof based on the well-ordering of the positive integers rather than the FTA: To begin with, we observe that if $\sqrt{2}$ is rational, then there is some positive integer q such that q × …
Dick Palais's user avatar
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48 votes

Extremely messy proofs

One nice example (from topology) is Tychonoff's Theorem (that a product of compact spaces is compact). No matter how many times I see it, I find the classic proof based on the (Alexandre Subbase Lemma …
68 votes
Accepted

Is "Cartan's magic formula" due to Élie or Henri?

Élie for sure. The formula is derived in Les systèmes differentiels extérieurs et leur applications géométriques which was probably written before Henri was born. BTW, here is a very short proof that …
Dick Palais's user avatar
  • 15.3k
2 votes

History of the triangle inequality

Here is a suggestion, to get the idea across in an informal way---it is what I always tell the students when I introduce the triangle inequality: I tell them that its essential content, and the way it …
Dick Palais's user avatar
  • 15.3k
56 votes

What is the situation with Hilbert's Fifth Problem?

The OP says: " ...Recently, Palais wrote about it in the Notices but he only treats the old story from the 1950s and seems not to be aware of Olver’s facts." Actually, I am aware of Olver's work and …
Dick Palais's user avatar
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15 votes

Old books still used

Spivak's five volume "Comprehensive Introduction to Differential Geometry" still gets a lot of use---particularly the first two volumes.
24 votes

What would you want to see at the Museum of Mathematics?

I have been involved with an online Mathematical Museum (called unsurprisingly The Virtual Math Museum, and located at http://VirtualMathMuseum.org). There is also an interactive version in the form o …
83 votes
Accepted

What if Current Foundations of Mathematics are Inconsistent?

The talk in question was given as part of a celebration (this past weekend) of the 80th anniversary of the founding of the Institute for Advanced Study in Princeton. As you might guess there were quit …
6 votes

Great mathematics books by pre-modern authors

Well, it bears a copyright date of 1902, but I think Eduoard Goursat's Cours D'Analyse is such an excellent text that it should be mentioned. I have the English translation, Mathematical Analysis, tra …
18 votes
1 answer
859 views

What sort of models did Bolyai and Lobachevsky use to demonstrate the consistency of their m...

As is well-known, in the 1820s both Bolyai and Lobachevsky showed, at long last, the independence of the Parallel Postulate from the rest of the axioms of Euclidean geometry by developing what we now …
Dick Palais's user avatar
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9 votes

Most memorable titles

I hope it is OK to mention "A Disorienting Look at Euler's Theorem on the Axis of a Rotation" even if I am a joint author, particularly if I admit that none of the authors thought up the cute title--- …