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 very book from which the whole list of a hundred and eight is taken: Rāma names all the upaniṣads to Hanumān and explains how they differ from one another. Here too is the teaching on the four kinds of liberation, and which of them is highest.