The Road Ahead
I think that’s about enough of the representation theory of the symmetric groups for now. There’s a lot more to say, but we’ve been at this for months and I’m itching for something new.
I’m thinking next up is some differential geometry, although I’ll have to take a little side trip to cover some basic differential equations before too long. I am still looking for a good reference that gets straight to the basic existence and uniqueness theorems of differential equations. If anyone has any suggestions, I’m all ears.
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The Unapologetic Mathematician 
That would be cool, maybe towards getting people towards able to understand the basics of GR? I suspect, sigh, that I’d fall off the wagon pretty soon, as usual, since what I really think I ought to learn about ATM is strong monads ….
My vote is for something about differential geometry.
I recommend Hurewitz’s little book “Lectures on Ordinary Differential Equations”, which begins with a beautiful treatment of the basic existence and uniqueness theorems (with a couple of different proofs, plus some things that lots of people don’t know, like that you can prove existence [but not uniqueness] without needing a Lipschitz condition).
Sounds good, Andy. Unfortunately it doesn’t seem to be in print, and I no longer have easy access to an academic library.
What book would you pick to teach an upper-level undergrad ODEs class?
I would be interested in seeing your approach. I studied ODEs, curves and surfaces last term and I am currently starting manifolds.
My professor didn’t use a book, he made his own approach to the existence theorems via functional analysis techniques.
I’ve really enjoyed the Strogatz book (non-linear dynamics and chaos) — easy read.
No comments but I just wanted to say that I am interested to hear your take on differential geometry. I am currently trying to learn a little myself.
You might check out Arnol’d:
The approach is geometric. After an initial chapter of examples, he gets down to the first existence and uniquenss theorem on page 36 (of my 1992 edition). Lots of diagrams, lots of applications to mechanics, which you may or may not be interested in.
Thanks, Santo. I do generally like Arnol’d, and geometry besides.
Just to make sure: his e/u theorems are in real vector spaces (though with one time dimension for derivatives, of course), correct?
John, yes, Arnol’d deals with real vector spaces, and almost entirely with just two-dimensions. Since his book is loaded with mechancis applications, the two dimensions are usually one space dimension and one time dimension.
I devoted quite some time to studying the representation theory of symmetric groups when working on my thesis, so your series of posts on this topic (excellent, as always) was a nostalgic trip down memory lane for me. Thanks!
Two dimensions is actually the important one. If you can prove it in two dimensions you can prove it in
dimensions. The proofs for one dimension don’t always clearly generalize, since 
matrices are just numbers.
An online favorite, Chapter 6 of Loomis and Sternberg:
Another suggestion is
from page 60 on.
Were you planning on covering any topics on Differential Manifolds? Just wondering… Also, I just discovered your blog and I have really enjoyed it –especially, the representation theory posts.
I was bryguy, but having a real job and another major hobby has put a major dent in my ability to maintain this one…