Collection of Qi (氣斂) from the Five Key Words (五字訣)

三,曰氣斂

氣勢散漫，便無含蓄，身易散亂，務使氣斂入脊骨。呼吸通靈,周身罔間。吸，為合為蓄；呼，為開為發。蓋吸則自然提得起，亦擎得人起；呼則自然沉得下，亦放得人出。此是以意運氣，非以力使氣也。

李亦畬

"Third saying: collection of Qi
If the Qi and Jin are disorganized, it is not contained. The body is easily scattered, it is possible from the exterior to make the Qi enter and control the spine. The breathing is smooth, there is no gap in the whole body. To inhale is to gather, it is as storing up; to exhale is to open, it is as emitting. Inhalation naturally lifts (the Qi) allowing the rise (of the spirit of vitality); it can also lift the opponent. Exhalation naturally sink (the Qi) allowing it to keep down; it can also release towards the opponent. This means that Yi guides Qi, one should not use Li to employ Qi."

By Lǐ Yìyú (李亦畬), based on the translation by by Yang Jwing Ming (楊俊敏) presented in the book Tai Chi Secrets of the Wu/Li Style (太極拳武李氏先哲秘要) and various translations on the internet

Thirty-first Secret Song (歌訣三十一) from the The Thirty-Six Songs of Baguazhang (八卦掌三十六歌) Trigésima Primeira Canção Secreta (歌訣三十一) das Trinta e Seis Canções do Bāguàzhăng (八卦掌三十六歌)

歌訣三十一

人持利器我不忙，
飛劍遙遙到身旁。
看他來路哼哈避，
邪不勝正語頗良。

"I am in no hurry if the opponent holds a sharp weapon,
The flying sword reaches my side from a distance.
Watch its coming trajectory and use the Hen and Ha sounds to avoid it,
That evil cannot match the just is a rather good saying."

Based on the translations by Yang Jwing Ming (楊俊敏) and Liang Shou You (梁守渝) in "Baguazhang - Theory and Applications" (峨嵋八卦掌) and by Frank Allen and Tina Chunna Zhang in "The Whirling Circles of Ba Gua Zhang"

""

Baseado na tradução de Yang Jwing Ming (楊俊敏) e Liang Shou You (梁守渝) apresentada em "Baguazhang - Theory and Applications" (峨嵋八卦掌) e na tradução de Frank Allen e Tina Chunna Zhang em "The Whirling Circles of Ba Gua Zhang".

The Song of Mutual Destruction (相剋歌) by Jiāng Róngqiáo (薑容樵)

相剋歌

劈能克崩崩克橫，
橫能克鑽鑽克炮，
炮能克劈歸易理，
不外五行求奧妙。

薑容樵

"Pi is able to overcome Beng; Beng is able to overcome Heng.
Heng is able to overcome Zuan; Zuan is able to overcome Pao.
Pao is able to overcome Pi; this belongs to the change principle.
These subtilities are not beyond the five elements."

From the book Xing Yi Mother Fists (形意母拳), by Jiāng Róngqiáo (薑容樵), based on the translation by Joseph Crandall

Excerpt from Attack by Stratagem (虛實) in The Art of War (兵法)

知彼知己，百戰不殆；不知彼而知己，一勝一負；不知彼，不知己，每戰必敗。

孫子

"If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle."

Unless noted otherwise, all quotations of classical texts and accompanying translations come from the Chinese Text Project

Proper Treatment without Defects (對待無病抗) by Yáng​ Bān​hóu​ (楊班侯)

對待無病

頂，匾，丟，抗，失於對待也。所以為之病者，既失粘黏連隨，何以獲知覺運動?既不知己，焉能知人?
所謂對待者，不以頂匾丟抗相對於人也，要以粘黏連隨等待於人也。能如是，不但無對待之病，知覺運動自然得矣。可以進於懂勁之功矣。

楊班侯

"Go Against, Deficiency, Lose and Resist means missing proper treatment. The reason is that if one loses attach, adhere, connect and follow, how can one attain consciousness in movement? If one is not able to be aware of it on oneself, how can one be aware of it on the opponent?
What is called proper treatment is not to use Go Against, Deficiency, Lose and Resist with the opponent. It is capital to use attach, adhere, connect and follow to match the opponent. Being able to do so not only there are no defects on the manners, consciousness in movement will be obtained naturally. It will then be possible to progress in the practice of Understanding Jin."

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)