The Upaniṣads — the philosophical core of the Vedic tradition, revealing the nature of Brahman, the Ātman, knowledge, action and liberation. The ten principal Upaniṣads together with select minor Vaiṣṇava Upaniṣads.
"The Book of the Eye": first a rite for the sight and a hymn to the sun, then seven stages of knowledge, from the first desire for truth to a state where nothing more is left to desire. These stages became a commonplace in Indian literature.