These trills always drove me crazy. Unlike math where rules are absolute, rules in music appear arbitrary.

I added English subtitles (not the "automatic" one). Might be able to apply translations. Also, did not do as I said with the Bach and Mozart. Reason is it appears those who used these tutorials are well on their way to reading music without further lessons from me. I finished Czerny's Opus 599. That will serve well as a continuation

https://sites.google.com/site/pianoan...

Masterclass with pianist Laszlo Gyimesi on trills:    • Piano Masterclass | Two types of trills