Another very influential concept unique to Mahāyāna is that of "Buddha-nature" ("buddhadhātu") or "Tathagata-womb" ("tathāgatagarbha"). Buddha-nature is a concept found in some 1st-millennium CE Buddhist texts, such as the "Tathāgatagarbha sūtras". According to Paul Williams these Sutras suggest that 'all sentient beings contain a Tathagata' as their 'essence, core inner nature, Self'. According to Karl Brunnholzl "the earliest mahayana sutras that are based on and discuss the notion of tathāgatagarbha as the buddha potential that is innate in all sentient beings began to appear in written form in the late second and early third century." For some, the doctrine seems to conflict with the Buddhist anatta doctrine (non-Self), leading scholars to posit that the "Tathāgatagarbha Sutras" were written to promote Buddhism to non-Buddhists. This can be seen in texts like the "Laṅkāvatāra Sūtra", which state that Buddha-nature is taught to help those who have fear when they listen to the teaching of anatta. Buddhist texts like the "Ratnagotravibhāga" clarify that the "Self" implied in "Tathagatagarbha" doctrine is actually "not-Self". Various interpretations of the concept have been advanced by Buddhist thinkers throughout the history of Buddhist thought and most attempt to avoid anything like the Hindu Atman doctrine.