 Yu Yan’s learned commentary contains quotations from about one hundred different texts, and is accompanied by philological notes on variants found in earlier editions.The Neidan commentary by Chen Zhixu 陳致虛 (1290-ca.1368) is entitled "Zhouyi cantong qi zhujie" 周易參同契注解 (Commentary and Explication of the "Cantong qi") and dates from ca.