Most temple books tie this marriage stick to a folk romance about Li Dan, the Tang prince who became Emperor Ruizong. In the legend, pushed aside when Empress Wu took the throne, he lived for a time as a commoner and met a village girl, Hu Fengjiao. Each had been born holding half of a square seal, and when they pressed the halves together the pieces matched, proof that they were meant for each other. The tale is staged in the Chu opera of Hubei as The Matching Seals. Two halves made whole is precisely the poem's yin and yang joined by heaven, which is why the stick is upper. Other editions name the Song philosopher Shao Yong, who worked out the numbers of yin and yang.