How did the number of less yin and less yang come from?

Shaoyin and Shaoyang are both one of the four elephants. Easy to have Tai Chi means giving birth to two instruments, two instruments giving birth to four elephants, and four elephants giving birth to gossip. In the gossip, do one, change two, stay three, shake four, train five, talk six, get seven, and get eight. Among them, dryness, intercourse, separation and shock are yang, while Xun, Kan, Gen and Kun are yin. Dry, exchange for the sun, away from, earthquake for shaoyang (that is, the number of shaoyang), gen, Kun for the lunar; Xun and Kan are shaoyin (that is, the number of shaoyang).