https://highpeakspureearth.com/the-sound-of-vultures-wings-the-tibetan-buddhist-chod-ritual-practice-of-the-female-buddha-machik-labdron-by-jeffrey-w-cupchik/
The Sound of Vultures' Wings: The Tibetan Buddhist Chod Ritual Practice of the Female Buddha Machik Labdron By Jeffrey W. Cupchik