In Unit 30, we looked at Dirichlet's proof. It is a classic which is
taught to any mathematician. (I learned it also as a student.
see the outline).
The proof appears in many places. The pure Fourier related books like Katznelson (1968) or
Koerner (1988) embed it into more theory which makes the extraction of the proof harder.
Below are the pages in the book of David Bressoud "A radical approach to real analysis"
giving the proof.
It is a bit more detailed than our Unit 30 handout,
which does it in 2 pages.
Image source: Assassins Creed Unity trailer.
