Counting with symmetry is covered in Week 6, Week 7, Week 8, Week 9, and Week 10, in the same order as this year.
For convenience, here are last year’s class notes as a single file: S21 Counting with symmetry
A complete set of video lectures from Spring 2021 are available as a supplemental resource (login required):
This link can also be found on our CourseWorks Home Page. The corresponding video lectures for counting with symmetry are February 18 through March 23.