According to Chen Yinque, the four tones were developed according to the Indian theory of three tones, which was completely summarized by Zhou Qing and Shen Yue, and then dualized by Wang Rong, Tamia Liu and jing yuan, and the flat tone was born. How many poems have Wang Rong, Tamia Liu and jing yuan counted and how many mistakes have they made? Wang Rong and others are most likely to count the poems of the Han, Wei, Southern and Northern Dynasties. Other people who invented Pingping also studied a few poems in the early Tang Dynasty, while the poems in the Han, Wei, Southern and Northern Dynasties were mainly five-character poems. Coupled with the limited research data at that time, the people who invented Pingping never read more than 10000 seven-character poems. As we know, there were five tones in ancient times: even tone, rising tone, rising tone, falling tone and entering tone. If you write a seven-character poem, each word may be one of the five tones. If it is raised to the seventh power of 5, there are 5× 5× 5× 5× 5× 5 = 78125 tone combinations. Suppose a tone combination corresponds to 1.
In 7 sentences, XaXbXcX, a may be flat or even voiced, b may be flat or even voiced, and c may be flat or even voiced. In this way, we can write seven sentences at will, and abc's octave (2x2x2) may be flat, flat, flat and even voiced.
Mathematically speaking, leveling is one-sided.