You can download problem set 1 here:
https://matherialien.jimdofree.com/
00:00 Introduction and overview
02:10 What are symmetries of a triangle?
07:23 D_3 and the composition of symmetries
12:55 Properties of composition in D_3
21:05 D_3 is a noncommutative group
25:36 Please comment
26:42 Do the exercises!
image of Abel from
https://upload.wikimedia.org/wikipedia/commons/thumb/8/80/Niels_Henrik_Abel.jpg/220px-Niels_Henrik_Abel.jpg