This means that in all nuclear hexagrams lines 2 and 4 are similar, and lines 3 and 5 are similar. So if line 2 is yang, line 4 is also yang. Like in hex.40 at left.
Only 16 hexagrams have this set of similar lines: 1, 2, 23, 24, 27, 28, 37, 38, 39, 40, 43, 44, 53, 54, 63, and 64. They are also nuclears.
For hex. 40 these 4 hexagrams are
40, 64, 54 and 38. In this case hex.40 also has hex.40 as nuclear. This is only the case with hexagrams which are nuclears themselves for other hexagrams.
The nuclear of hex.3 is 16. Hex.16's nuclear is 23. But the four hexagrams which share 23 as nuclear are 3, 8, 20 and 42. No 23 there.
A list for finding the nuclears.
When finding the nuclear, that means that you shove lines 2 and 4 together and lines 3 and 5. Relations and decisions for 2 and 4. Emotions and connections for 3 and 5. That must have a meaning.
Line 3 is trigramline earth and hexagramline heaven. It is the combination of man and heaven, man and his spirit: emotions. Now this line gets connected with some kind of complementary line 5, man in the realm of spirit.
Quality can be surroundings, hormones, anything which affects how or in what creatures or things are affected or behave.
In the nuclear the two lines, which overlap each other now, are complementary. Line 3, heaven-man with line 5, man-heaven. Line 2, man-earth with line 4 earth-man. Man lives on earth, but there is also earth in man: sense of reality, inner connection with tangible surroundings.
So there is a sense of mutual connection between man and the earth, and also between man and heaven. How does this make sense in a hexagram?
Eg hexagrams 3, 8, 20 and 42, the "family" of their common nuclear hex. 23.
According to Hilary the nuclear family shows "the potential inside the cast hexagram, but also their inner work". So 3, 8, 20 and 42 are potential and work of 23. Which does make some sense. Pruning a rosebush means new beginnings, an overview of how you prune, and increasing the roses. Only what hex.8 does is a bit unclear in this family.