Expository notes
Here are some expository notes. I make no claim of originality or even correctness(!), but they may be of interest.
- Lagrange's four square theorem via convex geometry (6/21/2023)
Every nonnegative integer can be written as a sum of four squares. This note derives this from Minkowski's theorem on lattice points in centrally symmetric convex sets.
- The Ritt–Raudenbush basis theorem (2/19/2023)
An analogue of the Hilbert basis theorem in differential algebra.
- Dickson invariants (3/17/2011)
Generators for the ring of invariants of the general linear group over a finite field; roughly speaking these are a q-analogue of elementary symmetric polynomials.
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