Complex sentence: The Krishn or the Taittiriya is the older book and the Sukla or the Vajasaneya is a later revelation to sage Yajnavalkya from Surya, the Sun-God.
Split into simpler sentences: The Krishn or the Taittiriya is the older book. While the Sukla or the Vajasaneya is a later revelation to sage ajnavalkya by Suryadev, the Sun-God.