preface
In Qiu Zhao'ao's "Detailed Notes on Du Shi", there is a paragraph that mentions Shen Yue's four voices and eight diseases, especially the explanation of several forms of flat head and tail.
There are three explanations for the flat head and three explanations for the upper tail.

First, the late verse gradually becomes more and more detailed in poetry
The Detailed Notes on Du Shi mentions that of Du Fu's more than one hundred seven laws, only four of them have the problem of ending:
Li Tian's birthday: Shaoling Seven Laws one hundred and sixty songs, only four stacked with 仄 characters, such as the "Jiangcun" poem, even the use of bureau, the word for things, the examination of his original "many diseases must only be drugs" as "fortunate to have the deceased to divide the rice", yu bureau characters do not overlap. The poem "Value on the River" uses the words Xing and Fishing. Kao Huang He Ben, "old psalm hun man xing" as "old psalm and rambling", yu fishing words do not overlap. The poem "Qiu Xing" uses the words "moon" and black, and the yellow crane ben, "Weaver Machine Silk Void Night Moon" is "Weaver Machine Silk Virtual Moon Night", and the black characters are not stacked. It can be seen that "the late festival gradually becomes more and more detailed in the poetry", and where the tail is sung, it is not a violation of each other.
Li Tiansheng pointed out Li Yindu in the late Qing Dynasty, and his statistics are not very accurate, but the meaning of his expression deserves our attention.
Li Yindu said that Du Fu's "late festival gradually became more and more detailed in poetry", which reflected that Du Fu would not make the mistake of ending his poems. He gave four examples, saying that only 4 of Du Fu's 160 Seven Laws committed the disease of the upper tail.
But these four songs, each with a different version, according to the other version, do not commit the disease of the tail. For example, "Gangchon":
Qingjiang is a song hugging the village stream, and Changxiajiang Village is quiet.
Since going to the hall on the swallow, blind date close to the water gulls.
The old wife draws paper as a chess piece[ game], and the child knocks the needle as a fishing hook.
The only medicine [thing] required for many diseases, and the micro-body is even more important.
Bureaus and things are all upper-sound words, committing the disease of the tail. However, there is another version of this poem, that is, the fifth sentence is: "Fortunately there are deceased people who divide the rice", rice, upper sound, thing, into the sound, avoiding the upper tail.
Therefore, Li Yindu believes that Du Fu may have modified the poem, that is, "fortunately there are deceased people to divide the rice" is the final version, and this version avoids the upper end.
Therefore, he believes that Du Fu's "late festival gradually becomes more and more detailed in poetry" is worthy of the name.
Regarding the upper tail, it is one of the eight diseases of Shen Yue, and among the eight diseases, the flat head and the upper tail are issues that must be paid attention to when composing rhythmic poems. But there are different explanations for the flat head and tail.
Qiu Zhao'ao, in the Detailed Notes on Du Shi, gave examples of these different interpretations.
Two or three upper tails
1. The upper end of the explanation in the theory of the secretarial office of the mirror
The so-called upper end, the last word of the upper sentence and the last word of the next sentence, both use a flat voice. Although the rhyme is different and the sound is the same, it is a mistake on the tail. For example, the ancient poem "There are tall buildings in the northwest, and the upper and floating clouds are in unison", the building and qi are all flat, and the sound of "the court has a rue, and the green leaves contain Danrong", and the durian and rong are also peaceful. "Du Shi Detailed Notes"
This explanation comes from the explanation of Shen Yue's eight diseases in The Secret House of Wenjing.
If the ending word of the upper link is a flat sound, the ending word of the lower link is also a flat sound, but it does not rhyme, which is the disease of the flat head.
In the Grammatical poem, the first sentence rhymes, not a flat head, and the 3rd, 5th, and 7th sentences end with a slang sound, so it is not a flat head. It can be seen that the Vinaya appeared in full compliance with this flat-headed rule.
2, every phrase eio
Another sentence with three ends is used in the same voice, which is also the upper end. As the ancient poem "The guest comes from afar, and leaves me a book." The upper words of Sauvignon Blanc, the next words of long parting", come and think quietly. Another example is "the new system of Qi Qi Su, as clean as frost and snow." Cut into acacia fans, reunion like autumn moon", vegetarian, fan are to go to the sound, but also guilty of the tail.
In the seven laws, such as Du Shi's "Spring Wine Glass Thick Amber Thin" and "Mistakenly Suspect maotang into the river foothills", the same system into the sound. Wang Weishi's "New Fengshu Li Pedestrian degree" and "WenDao Ganquan can dedicate endowments" rhyme with each other, both of which are guilty of the tail. "Du Shi Detailed Notes"
The first and third sentences, the third and fifth sentences, the fifth and seventh sentences, if they are homophonous, are also the upper end. For example, Wang Wei's Seven Laws of Harmony and Taichang Wei's Master Book Of Wulang Wentang Fables:
The Han lord left the palace to receive the terrace, and the Qin River was half open at sunset.
The green mountains are surrounded by Zhu Qi, and the green streams come from the Jade Hall.
New Mapletree lane pedestrians [degree], Xiaoyuan City side hunting ride back.
Wen Dao Ganquan can offer [endowment], suspense knows the unique son Yuncai.
Degrees, endowments, are all de-sounding. This is the upper tail. That is, in the first part, Li Yindu said that Du Fu's four-head and tail phenomenon.
3, Ashi-a-tail
Another example is Du's "Qiu Xing" poem "Looking west to Yaochi descends to the Queen Mother, and in the east comes purple qi full of letters." The cloud moves the pheasant tail to open the palace fan, and the sun goes around the dragon scales to recognize the holy face", the queen mother, the letter guan, the palace fan, the holy face, all at the end of the sentence, it is inevitable to overlap the foot, but also to commit the tail. "Du Shi Detailed Notes"
This one has an upper tail, due to the difference between the first two. Much like the four flat heads we usually say (the beginning of the four sentences is the same), the example here is the end of the sentence. An example of Du Shi's Detailed Notes is one of Du Fu's "Autumn Xing":
The fish dragon is lonely and the autumn river is cold, and the homeland is peaceful and thoughtful.
Penglai Palace que to the South Mountain, revealing the golden stem Xiao Han.
Looking west to Yaochi descending [Queen Mother], east to purple qi full of [Hanguan].
The cloud shifts the pheasant tail to open the [palace fan], and the sun goes around the dragon scales to recognize the [holy face].
Three, three kinds of flat heads
1. The beginning of the sentence is flat with the same voice
The so-called flat-headed person, the first two words in the first sentence, and the two words on the last sentence are the same, such as the ancient poem "Today's good banquet, joy is difficult to be Chen". This joy is the same sound, the day and the music are the same sound, it is a flat head. Another example is "the obscure first scene of the clouds, the late flying snow of Danchi", "the floating cloak gathers and disperses, blowing and condensing its might", the two words on the four sentences are flat, and they are flat heads. "Du Shi Detailed Notes"
2. The structure of the first word of the sentence is the same
Another example is the Zhou Wang's poem "High box illuminates mica, and strong horses are decorated as skulls." Single cloth fire raccoon cloth, sword water essence beads", four sentences stacked with four things, and each thing uses a virtual and a real literal, also a flat head. "Du Shi Detailed Notes"
In the Northern Zhou Dynasty Wang's "Sunrise Southeast Corner", the four words of high box, strong horse, single clothes, and sharp sword are all partial orthopoical phrases, the first word is a modifier: high, strong, single, and interest, and the second word is the central language: box, horse, clothing, and sword.
3. The first sentence is stacked to attract people's names
Another example is Du Zhishi's poem "Yi Zhi is a concubine, and Lü Wang is a pole." Yiwu trapped the vendor, Ning Qi sighed at the cow. Eat its place to supervise the door, Huaiyin hunger does not eat", superimposed on the ancients, all at the beginning of the sentence, is also a flat head also. "Du Shi Detailed Notes"
In fact, this one is similar to the second, and the capital of the sentence is a personal name. Here is an example of the late Han Dynasty Three Kingdoms poet Du Zhi's "Gift of Qiu Jian poems", but it is more important to avoid when composing rhythmic poems.
The four flat heads we are talking about now include the second and third phenomena.
Conclusion
The previous evaluation of Du Fu's "late festival gradually became more and more detailed in poetry" refers to Du Fu's increasing attention to the avoidance of various poetic diseases.
Regarding the four flat heads and the question of the end of the sentence, it is actually said that the poem should pay attention to changes and avoid similarities.
@Old Street Taste
In the sentence, the three servants are bent at the end of the sentence, and there are origins everywhere, and Du Fu's Seven Laws "Title Zhang's Hermitage" is appreciated