Book 7, embeds sutras for accurate pronunciation after the terse phrases "On Letters", "On Accents", "On Quantity", "On Delivery", and "On Euphonic Laws". The fourth and often the last layer of philosophical, speculative text in the Vedas, the Upanishads, too have embedded sutras such as those found in the Taittiriya Upanishad. The compendium of ancient Vedic sutra literature that has survived, in full or fragments, includes the Kalpa Sutras, Smarta Sutras, Srauta Sutras, Dharma Sutras, Grhya Sutras, and Sulba Sutras. Other fields for which ancient sutras are known include etymology, phonetics, and grammar. Post-vedic sutras Some examples of sutra texts in various schools of Hindu philosophy include Brahma Sutras (or Vedanta Sutra) – a Sanskrit text, composed by Badarayana, likely sometime between 200 BCE to 200 CE. The text contains 555 sutras in four chapters that summarize the philosophical and spiritual ideas in the Upanishads. It is one of the foundational texts of the Vedānta school of Hindu philosophy. Yoga Sutras – contains 196 sutras on Yoga including the eight limbs and meditation. The Yoga Sutras were compiled around 400 CE by Patanjali, taking materials about yoga from older traditions. The text has been highly influential on Indian culture and spiritual traditions, and it is among the most translated ancient Indian text in the medieval era, having been translated into about forty Indian languages. Samkhya Sutra – is a collection of major Sanskrit texts of the Samkhya school of Hindu philosophy, including the sutras on dualism of Kapila. It consists of six books with 526 sutras. Vaisheshika Sutra – the foundational text of the Vaisheshika school of Hinduism, dated to between the 4th century BCE and 1st century BCE, authored by Kanada. With 370 sutras, it aphoristically teaches non-theistic naturalism, epistemology, and its metaphysics. The first two sutras of the text expand as, "Now an explanation of Dharma; The means to prosperity and salvation is Dharma." Nyaya Sutras – an ancient text of Nyaya school of Hindu philosophy composed by Akṣapada Gautama, sometime between the 6th century BCE and 2nd century CE. It is notable for focusing on knowledge and logic, and making no mention of Vedic rituals. The text includes 528 aphoristic sutras, about rules of reason, logic, epistemology, and metaphysics. These sutras are divided into five books, with two chapters in each book. The first book is structured as a general introduction and table of contents of sixteen