Todayand#8217;s FBA Dharmabyte, by Sangharakshita, is an introduction to what is likely the most important of the four mula-yogas, the indispensable preparatory practices of the Vajrayana devotee. and#8220;Vajrasattva: Purificationand#8221; is an excerpt from The Four Foundation Yogas of the Tibetan Buddhist Tantra, given in 1968 as part of the series An Introduction to Tibetan Buddhism.