the end of the Vedic period. The Upanishads are largely philosophical works, some in dialogue form. They are the foundation of Hindu philosophical thought and its diverse traditions. Of the Vedic corpus, they alone are widely known, and the central ideas of the Upanishads are still influential in Hinduism. The texts considered "Vedic" in the sense of "corollaries of the Vedas" are less clearly defined, and may include numerous post-Vedic texts such as the later Upanishads and the Sutra literature, such as Shrauta Sutras and Gryha Sutras, which are smriti texts. Together, the Vedas and these Sutras form part of the Vedic Sanskrit corpus. While production of Brahmanas and Aranyakas ceased with the end of the Vedic period, additional Upanishads were composed after the end of the Vedic period. The Brahmanas, Aranyakas, and Upanishads, among other things, interpret and discuss the Samhitas in philosophical and metaphorical ways to explore abstract concepts such as the Absolute (Brahman), and the soul or the self (Atman), introducing Vedanta philosophy, one of the major trends of later Hinduism. In other parts, they show evolution of ideas, such as from actual sacrifice to symbolic sacrifice, and of spirituality in the Upanishads. This has inspired later Hindu scholars such as Adi Shankara to classify each Veda into karma-kanda (कर्म खण्ड, action/sacrificial ritual-related sections, the Samhitas and Brahmanas); and jnana-kanda (ज्ञान खण्ड, knowledge/spirituality-related sections, mainly the Upanishads'). Śruti and smriti Vedas are ("what is heard"), distinguishing them from other religious texts, which are called ("what is remembered"). This indigenous system of categorization was adopted by Max Müller and, while it is subject to some debate, it is still widely used. As Axel Michaels explains: Among the widely known śrutis include the Vedas and their embedded texts—the Samhitas, the Upanishads, the Brahmanas and the Aranyakas. The well-known smṛtis include Bhagavad Gita, Bhagavata Purana and the epics Ramayana and Mahabharata, amongst others. Authorship Hindus consider the Vedas to be apauruṣeyā, which means "not of a man, superhuman" and "impersonal, authorless." The Vedas, for orthodox Indian theologians, are considered revelations seen by ancient sages after intense meditation, and texts that have been more carefully preserved since ancient times. In the Hindu Epic Mahabharata, the creation of Vedas is credited to Brahma. The Vedic hymns themselves assert that they were skillfully created by Rishis (sages), after inspired creativity, just as a carpenter builds a chariot. The oldest part of the Rig