confused about the pruning rules in jps3d

[wilsionhuang]

Hi , i am confused about the force neiberhood of norm1 in jps3d.
In the code, the force neiberhood is the eight neiberhood node around the natual node in same plane. but if we use the jps2d rule: len (< parent ( x ) , . . . ., n >\ x ) ≤ len (< parent ( x ) , x, n >), the force neiberhood should be other node. see the node that marked as red line below.
Can you explain the pure rule in jps3d, thank you.