Master Chen demonstrated Lu, Cai, and Lie with in-with-elbow in “Shake the Pole”. These three belong to the same group.
Lu 捋 – You grab the opponent’s arm, pull him in, and throw him onto the other side. There is no severance of the arm in this case.
Cai 採 – You grab the opponent’s arm, and pull on it quickly to sever it at the shoulder. This is like plucking a flower.
Lie 挒- You grab the opponent’s arm, and pull him in. He hits your body, which provides a stop to the incoming force. This also allows the arm to be severed at the shoulder.