Chu Shih-Chieh, also known as Zhu Shie-jie, wrote two important texts in 1299 and 1303. The first Introduction to Mathematical Studies was intended for beginners. The second book Precious Mirror of the Four Elements marks the peak of Chinese mathematics and it was a long time before further progress was made in China. The book contains a transformation method for solving equations (used up to degree 14) rediscovered by Horner and Ruffini. It also contains the Pascal triangle (discovered in China earlier) and gives formulas for 1 + 2 + 3 + 4 + ... , 1 + 3 + 6 + 10 + ... , 1 + 4 + 10 + 20... , 1 + 5 + 15 + 35 + ... , 1 + 6 + 21 + 56 + ... .