[机] alternation of multiplicities law

chóng fù xìng biàn huà dìng lǜ ㄔㄨㄥˊ ㄈㄨˋ ㄒㄧㄥˋ ㄅㄧㄢˋ ㄏㄨㄚˋ ㄉㄧㄥˋ lv4