The goal of "tapas" is to help focus the Brahmachari on meditation, observation of reality, reflection and spiritual rebirth. Brahmacharya and "tapasya" are interrelated, with the student life expected to simple and austere, dedicated to the learning. "Tapas" is a central concept in Jainism. It refers to the spiritual practice of body mortification, penance and austerities, in order to burn away past karma and stop producing new karma, thereby reaching "siddha" (liberating oneself). Ascetic "Tapas" among Jaina monks, both internal and external, is believed to be essential for spiritual growth and "kevalya" (moksha, liberation). The details of the "Tapas" practices vary between the different traditions within Jainism. The Jain text "Sarvarthasiddhi", a commentary by Pujyapada, claims that the Hindu Samkhya school emphasizes "knowledge only, no practices", while the Vaisheshikas emphasize "practices only, no knowledge" as part of "Tapas" and the means of reaching moksha. Another Jain text "Tattvartha Sutra", by Umaswati, in chapter 9, asserts that "Tapas" includes several kinds of meditation. The "Tapas" in Jainism include internal practices and external austerities. External "Tapas" include fasting, tolerating hardships inflicted by other people or animals, tolerating all discomfort from weather by nakedness or near nakedness and the lack of any possessions, lack of shelter, walking and wandering alone without fearing anything and without hurting anyone. The internal "Tapas" include words and inner thoughts (intent) that resonate with the external "Tapas" (action). The list of internal and external austerities in Jainism vary with the text and tradition, with "Tattvartha Sutra", "Uttaradhyayana Sutra" and "Bhagavati Sutra" stating:   In Jainism, "Tapas" implies a control on desires, and is a form a self purification. Mahavira, the 24th Tirthankara undertook ascetic "Tapas" for twelve years, after which he attained Kevala Jnana (liberating supreme knowledge). Ajivikas was another ancient Indian religion which survived through about 13th-century CE, but became extinct thereafter, in which "Tapas" was a central concept as a means of salvation.