The Song of Eight Words in Taiji’s Engagement with the Opponent (太極人盤八字歌) by Yáng​ Bān​hóu​ (楊班侯)

太極人盤八字歌

八卦正隅八字歌，十三之數不幾何。
幾何若是無平準，丟了腰頂氣歎哦。
不斷妄言只而宇，君臣骨肉細琢磨。
功夫內外均不斷，對待數兒豈錯他。
對行於人出自然，由茲往復於地天。
但求捨己無深病，上下進退永連綿。

楊班侯

"The eight trigrams, sides and corners, are the song of the eight words; the number thirteen, after all, is not too large.
It becomes complex if there is no balance and precision; the waist, the push upwards and the breathing will be lost, only to be lamented.
The saying on uninterrupted movement contains only two words; one shall refine the relations between the sovereign and the minister, the muscles and bones.
If in Gongfu the internal and external are uniform and uninterrupted all not broken, one cannot be wrong in sparring. The right answer to the opponent is to go out naturally; to follow him back and forth like heaven and earth.
Only seek to give up oneself without defects; the top and the bottom, advance and retreat, can be executed continuously forever."

Based on the translation by Yang Jwing Ming (楊俊敏) presented in the book Tai Chi Secrets of the Yang Style (太極拳楊氏先哲秘要)

Straighten the Nape; Lift the Crown. Buttocks Slip; Hold the Anus (順項提頂，溜臀收肛) from The Real Theory of Baguazhang (八卦掌真理篇) by Jiāng Róngqiáo (薑容樵)

順項提頂，溜臀收肛

順項是使頸項自然豎直，在鍛煉時不要仰頭，不要低頭，也不要左右歪斜。提頂是將下頦裡收，頭向上直頂。溜臀是將臀部下垂向裡收縮，在鍛煉時不要有絲毫的向後撅臀的現象產生。收肛是將肛門的肌肉予以收縮控制，不要使它放鬆。

薑容樵

"Straighten the nape means the neck becomes naturally upright; during the practice one should not raise or bow the head nor incline it left or right. To lift of the crown means the chin is collected in; the head pushes up and straighten the crown of the head. Buttocks slip means the buttocks will hang down and contract inward. During the practice one should not let the buttocks even to start to stick out backwards. To hold the anus means one must apply a controlled contraction to the rectal muscle; and not allow it to loosen."

From the book Bāguàzhăng Practice Method (八卦掌練習法), by Jiāng Róngqiáo (薑容樵), based on the translation by Joseph Crandall

Taiji Above and Below explained as Heaven and Earth (太極上下名天地) by Yáng​ Bān​hóu​ (楊班侯)

太極進退不已功

四手上下分天地，採列肘靠有由去。
採天靠地相應求，何患上下不既濟!
若使挒肘習遠離，迷了乾坤遺歎惜。
此說亦明天地盤，進用肘挒歸人字。

楊班侯

"Differentiating the four hands above below are like heaven and earth; pluck, split, elbow and bump have their source in this separation.
If pluck from heaven and bump from earth correspond and look for each other; one should not worry if above and below support each other!
If one creates the habit of using split and elbow separately, one will lament the unbalance between heaven and earth.
This also explains the circles of heaven and earth; to advance in the application of split and elbow one should return to the word “man”."

Based on the translation by Yang Jwing Ming (楊俊敏) presented in the book Tai Chi Secrets of the Yang Style (太極拳楊氏先哲秘要)

Quiescence (清) by Dài Běnxiào (戴本孝​)​

Féng​ Zhèng​bǎo​ (馮正寳) demonstrating Xíngyìquán (形意拳)