Wu Kecheng and his son Wu Jingluan 吳景鸞 (d. 1064) are not mentioned in other sources except in writings specialized on geomancy. It is said that the Wus hailed from Dexing 德興 in modern Jiangxu and that Wu Kecheng was a disciple of the Daoist master Chen Tuan 陳摶 (871-989). His son Wu Jingluan was able to rise to the state office of Director of Astronomy (sitian jianzheng 司天監正). For a while he was kept in prison because he had discussed a matter of an imperial mound on Mt. Niutou 牛頭山. After he was set free he feigned sickness and lived in a cave on Mt. Baiyun 白雲山. Before he died he gave his daughter a book, presumable the Waizhuan. His daughter, wife of Zhang Daoming 張道明, asked Liao Yu 廖瑀 (943-1018) to bring the text in a decent form.
The Tianyujing waizhuan is also called Wu Gong jiao zi shu 吳公教子書 "Book of Master Wu's instructions to his son". It is quite short and accompanied by charts of the so-called 48 camps, Sishiba ju tu 四十八局圖. The basic ideas of this text are derived from the books Qingnang aoyu 青囊奧語, Cuiguanpian 催官篇 and Yuchijing 玉尺經, particularly the concept of the "three culminations" (sanhe 三合), meaning a combination of trigrams (see Yijing 易經) with cyclical signs (see calendar) and one of the Five Agents 五行.
Is it said, for instance, that the cyclical combination gengwu 庚午 of the Celestial Stems (tiangan 天干) and Terrestrial Branches (dizhi 地支) was attributed to the camp of the agent huo 火 "fire", and that the dragon of the Branch yin (yinlong 寅龍) was leftwards wound to the Stem bing 丙, and rightwards to the Stem ding 丁. This deviates from older concepts, in which other Stems were related to the agent fire.
|艮 gen "mountain"||辛 xin||火 huo "fire"|
|坤 kun "Earth"||乙 yi||水 shui "water"|
|乾 qian "Heaven"||丁 ding||木 mu "wood"|
|巽 xun "wind"||癸 kui||金 jin "metal"|
The theory of relating certain trigrams and cyclical signs with agents ("elements") is a quite modern concept and not to be found earlier than the Ming period 明 (1368-1644). It must therefore be concluded that the text in the transmitted form must have been compiled during the Ming era, when the original meaning of the "three culminations" was already interpreted in a different way.