by Iswara
This upanishad belongs to Atharva Veda, the smallest upanishad out of 1180 upanishads having only 12 mantras. It also contains the maha vakya - "ayam atma brahma". The only upanishad which needs karika's to understand it completely, written by Sri Gaudapadacharya, the great guru of Sri Jagat Guru AdiShankaracharya. The main goal of this upanishad is to establish Advaita and "AUM_" pranava is the subject matter of the upanishad.