In regards to the three steps of Vishnu, Glucklich points out that in some legends of Vamana and the Asura-king Bali, that 'the first [step] covered the entire earth, the second covered the atmosphere, and the third measured heaven in its entirety'. M. Haug, in his translation of the Aitareya Brahmana (1.1.5) of the RigVeda, clarifies that the 'three worlds' often means the ground (earth), the air (atmosphere), and the sky (heavens). Three steps thus encompasses all of physical existence (although in some Puranic accounts Vamana does so in only two steps). D. Goodall also relates more a mystical interpretation of what 'three worlds' symbolises, as provided by the Brihadaranyaka Upanishad, including Mind, Speech, and Breath (see Upanishad section, below).