lgyō school (Chin. kuei-yang-tsung; Jap. igyō-shū); a school of Ch’an (Zen) that was among the “five houses-seven schools,” i.e., the great schools of the authentic Ch’an tradition. The name of the school derives from the initial characters of the Japanese names of its two founders, Kuei-shan Ling-yu (Jap., Isan Reiyū) and his dharma successor Yang-shan Hui-chi (Jap., Kyōzan Ejaku).
Typical for the method of instruction of the Igyō school was the use of a system of ninety seven symbols, each inscribed in a circle. This system, which is said to have originated with Hui-neng, the sixth patriarch of Ch’an (see also Tan-yuan Ying-chen), has not been preserved but did influence the development of the ten oxherding pictures (jūgyū-no-zu) as well as the five degrees (of enlightenment) of Master Tung-shan. It seems to have represented some sort of secret language through which persons with profound experience of Ch’an could communicate with each other concerning the basic principles of the teaching. Since the masters were aware that this system could easily degenerate into a mere formalized game, it was evidently transmitted to only a few students under a seal of strict secrecy. In the middle of the 10th century the Igyō lineage merged with the lineage of the Rinzai school and from that time no longer subsisted as an independent school.
Source: The Encyclopedia of Eastern Philosophy and Religion: Buddhism, Hinduism, Taoism, Zen. Shambhala Publications, Inc.
Books on lgyō school
External links: Kuei-shan Ling-yu (Isan Reiyū) / dharma / Yang-shan Hui-chi (Kyōzan Ejaku) / Hui-neng / Jūgyū(-no)-zu: Ten Oxen Pictures