Video cycle 2021

During the spring semester 2021, during the pandemic, I came in every Saturday to record some little movie about the upcoming lecture each. These videos were optional but I felt they can replace the lack of energy which a Zoom lecture brings. I have taught this class since 2010 and in the first years exclusively in a real class room setting. Update 2022: Here is the video cycle from 2022 which is done in slide format.
Trailer Unit 1 Syllabus Unit 2: Number Systems Unit 3: Geometry
Unit 4: Number Theory Unit 5: Algebra Unit 6: Calculus Unit 7: Logic
Unit 8: Probability Unit 9: Topology Unit 10: Analysis Unit 11: Cryptology
Unit 12: Dynamical system Unit 13: Computer Science