about the later part of the 3rd century CE, and is verifiable in Chinese translations of 1st millennium CE. Most scholars consider the tathāgatagarbha doctrine of an 'essential nature' in every living being is equivalent to 'Self', and it contradicts the "no self" (or no soul, no atman, anatta) doctrines in a vast majority of Buddhist texts, leading scholars to posit that the Tathagatagarbha Sutras were written to promote Buddhism to non-Buddhists. The Mahāyāna tradition thus often discusses nirvana with its concept of the tathāgatagarbha, the innate presence of Buddhahood. According to Alex Wayman, Buddha nature has its roots in the idea of an innately pure luminous mind (prabhasvara citta,) "which is only adventitiously covered over by defilements (agantukaklesa)" lead to the development of the concept of Buddha-nature, the idea that Buddha-hood is already innate, but not recognised. The tathāgatagarbha has numerous interpretations in the various schools of Mahāyāna and Vajrayana Buddhism. Indian Madhyamaka philosophers generally interpreted the theory as a description of emptiness and as a non implicative negation (a negation which leaves nothing un-negated). According to Karl Brunnholzl, early Indian Yogacaras like Asanga and Vasubandhu referred to the term as "nothing but suchness in the sense of twofold identitylessness". However some later Yogacarins like Ratnakarasanti considered it "equivalent to naturally luminous mind, nondual self-awareness." The debate as to whether tathāgatagarbha was just a way to refer to emptiness or whether it referred to some kind of mind or consciousness also resumed in Chinese Buddhism, with some Chinese Yogacarins, like Fazang and Ratnamati supporting the idea that it was an eternal non-dual mind, while Chinese Madhyamikas like Jizang rejecting this view and seeing tathāgatagarbha as emptiness and "the middle way." In some Tantric Buddhist texts such as the Samputa Tantra, nirvana is described as purified, non-dualistic 'superior mind'. In Tibetan Buddhist philosophy, the debate continues to this day. There are those like the Gelug school, who argue that tathāgatagarbha is just emptiness (described either as dharmadhatu, the nature of phenomena, or a nonimplicative negation). Then there are those who see it as the non-dual union of the mind's unconditioned emptiness and conditioned lucidity (the view of Gorampa of the Sakya school). Others such as the Jonang school and some Kagyu figures, see tathāgatagarbha as a kind of Absolute which "is empty of adventitious defilements which are intrinsically other than it, but is not empty of its own inherent existence".