Topology IV.b - homotopy theory

Homework/semi-flipped teaching: I am asking you this week to read the very beginning of Section 3 on the CW-approximation Theorem, only one page till we reach the statement of the theorem we will prove together next Tuesday. There are two lemmas about the connectivity of a pair obtained by attaching a cell to a space. It is useful to have the relative cellular approximation Theorem in mind, but the absolute one and the long exact sequence of a pair is often sufficient to understand the situation.

This corresponds to about 10 minutes of the corresponding video (Week 6, lecture 1), but I'm not sure if this includes the lemma in this version.