The Diamond Sutra (Vajracchedika Prajnaparamita, "the perfection of wisdom that cuts like a diamond/thunderbolt") is one of the most influential of the Mahayana "Perfection of Wisdom" scriptures, a concise text cast as a dialogue between the Buddha and his disciple Subhuti. Its teaching is the radical non-substantiality (emptiness, sunyata) of all things and all concepts, pressed through a series of self-undercutting formulas, that what is called a thing is precisely not that thing, and is therefore called that thing, designed to dissolve every fixed notion, including the notions of self, of beings, and even of the teaching itself; the practitioner is to act "without abiding" in any concept. It is especially treasured in the Zen/Chan tradition. The Diamond Sutra holds a further, material distinction: the copy recovered from the sealed cave-library at Dunhuang, now in the British Library, is a printed scroll dated to 868 CE, and is the earliest complete, dated printed book known to survive anywhere in the world.