Master Chen Zhonghua Online Lesson on Sep 24, 2021 - Kelvin Ho
Lever: one side goes down, but it actually needs to move, so the pivot keeps moving backward within the rod.
Book exercise: Not allowing the book to fall down with your hand and opponent's hand on it. One person pushs and pulls, the opponent matches the action with the elbow, shoulder, kua, feet.
Leader in 3-count circle
Six Sealing Four Closing: While the two knees are going up and down, they are restricted within a cylinder.
Source: https://practicalmethod.com/?p=78420