Liang Yi is the two poles of Yin and Yang. In Baguazhang, walking to the left (counterclockwise) is Yang, walking to the right (clockwise) is Yin. Sun Lu Tang associated the Single Palm Change to Liang Yi.
From the left Pushing Millstone Palm, toe-in with the right foot to begin the change. The torso posture does not change.
Toe-out with the right foot and turn the palms over so they are pushing in the direction of the change. This movement can look as if you are pushing with the arms but do not; maintain the torso and arm alignments and let the toe-out movement create the push. The eyes remain focused on the left hand.