vision of a syllable or symbol may leaven the realisation of the latent terma in the mind of the tertön. The process of hiding in the mind implies that the practitioner is to gain realisation in that life. At the time of terma concealment, a prophecy is generally made concerning the circumstances in which the teaching will be re-accessed. Especially in the case of an earth-terma, this usually includes a description of locality, and may specify certain ritual tools or objects which are required to be present, and the identities of any assistants and consorts who are required to accompany or assist the tertön. Though somewhat contentious, the kind of revealed teaching embodied in the terma system is based in solid Mahayana Buddhist traditions. The example of Nagarjuna is often cited; the Prajnaparamita teachings are traditionally said to have been conferred on Nagarjuna by the King of the nāgas, who had been guarding them at the bottom of a lake. Similarly, the Six Treatises of Asanga are considered to have been conferred on him by the Buddha Maitreya, whom he visited in Tushita heaven during a vision. "Pure visions" are pure teachings received from the vision of deities. These are not necessarily terma, because they do not require mindstream transmission from a guru to the practitioner experiencing the pure vision. The esoteric teachings resulting from pure vision are based on the tantras, and are sometimes considered as terma due to their merit. In Bön A terma tradition also exists in Bön. Most Bön termas were hidden during the period of decline under King Trisong Deutsen, and rediscovered around the 11th century. Teachings were hidden by masters such as Lishu Tagring and Drenpa Namkha, often inside Buddhist temples, as in Samye and Lhodrak. The three Treasures For the Bonpo, Gankyil denotes the three principal terma of Yungdrung Bon, the "Northern Treasure" (), the "Central Treasure" () and the "Southern Treasure" (). The Northern Treasure is compiled from texts revealed in Zhangzhung and northern Tibet, the Southern Treasure from texts revealed in Bhutan and the southern area of Tibet, and the Central Treasure from texts revealed in central Tibet close to Samye. A Cavern of Treasures A Cavern of Treasures () is a terma uncovered by Shenchen Luga () in the early eleventh century. Martin (n.d.: p. 21) identifies the importance of this scripture for studies of the Zhang-Zhung language: Cycles One