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.
Fourteen verses — a hymn to the one syllable and to the One named by it. One of the most compressed books: almost every word in it is a name, and all of them converge on Viṣṇu.