Topology IV.b - homotopy theory

Homework/Semi-flipped teaching. For the course on 18 March I would like you to read the course notes on the preparation for the PL-approximation Lemma (Chapter 3, pages 33-34). Alternatively you can watch the last 8 minutes from the video:

https://mediaspace.epfl.ch/media/Long+Exact+Sequence+in+Homotopy%2C+Lecture+04.2/0_z6fnxoe3

they concern cellular maps and polyhedra, and also the first 12 minutes of the next video:

https://mediaspace.epfl.ch/media/PL+map+Lemma%2C+Lecture05.1/0_92s1trl1

where we learn about PL maps and two useful constructions in the next proof. It can be useful to have a look at the next two minutes, but I will do a similar drawing at the beginning of the lecture.