Lay people are usually not permitted to give initiations if there are teachers with monastic vows within close proximity. The Gelug school developed a highly structured system of scholastic study which was based on the memorization and study of key texts as well as formal debate. The primary topics and texts used in study are:   Six commentaries by Tsongkhapa are also a prime source for the studies of the Gelug tradition, as follows:  According to Georges Dreyfus,  For each topic studied, the procedure is similar. The process starts with the heuristic memorization of the root text and sometimes of its commentaries. It continues with the interpretation of the root text through commentaries, and culminates in dialectical debate. After the study of the exoteric texts, a monk may then enter the esoteric study and practice of tantric texts, particularly the Guhyasamāja, Yamāntaka, and Cakrasamvara tantras. A monk who completes all his study may then attempt for a geshe degree, a rare and difficult title to obtain which can take 15 to 25 years to complete. Each Gelug monastery uses its own set of commentarial texts by different authors, known as monastic manuals (Tib. "yigcha"). The teachings of Tsongkhapa are seen as a protection against developing misconceptions in understanding and practice of Mahāyāna and Vajrayāna Buddhism. It is said that his true followers take "The Great Exposition of the Stages of the Path" as their heart teaching. "The Great Exposition of the Stages of the Path" was completely translated into English in a three volume set in 2004, under the title "The Great Treatise on the Stages of the Path to Enlightenment". The translation took 13 years to complete, and was undertaken by scholars at the Tibetan Buddhist Learning Center, a non-sectarian Tibetan Buddhist educational center in Washington, New Jersey. A translation is also available in Vietnamese. In 2008, the 14th Dalai Lama Tenzin Gyatso gave a historical five day teaching on the text at Lehigh University. Tsongkhapa founded the monastery of Ganden in 1409 as his main seat. Drepung Monastery was founded by Jamyang Choje, Sera Monastery was founded by Chöje Shakya Yeshe and the Gyalwa Gendün Drup founded Tashi Lhunpo Monastery. Before the Chinese occupation Ganden and Sera each had about 5,000 monks, while Drepung housed over 7,000.