Note 437 — Chapter XXVI
Reading edition
E.g. the beginning of the Chând. Up. about the syllable Om. See too the last section of the Aitareya Âran. The Yoga Upanishads analyse and explain Om and some Vishnuite Upanishads (Nṛisiṃha and Râmatâ-panîya) enlarge on the subject of letters and diagrams.