Four sections of tantra. Kriya, Charya, Yoga, and Anuttara Yoga. four classes of tantra: bya rgyud, Kriya; spyod rgyud, Charya tantra; rnal 'byor rgyud, yoga tantra; bla med rnal 'byor rgyud, Anuttara Yoga tantra. Kriya Tantra, Ubhaya. or Charya Tantra, Yoga Tantra, and Unsurpassed Yoga Tantra. activity tantra, engagement tantra, yoga tantra, and highest yoga tantra