(Spanda Kārikā): This “Composition on Vibration,” authored by either Vasugupta or (less likely) his chief disciple Kallata, is an independent commentary on the Shiva Sutras. It explains the notion of spanda (divine vibration), which is a central doctrine of Kashmir Shaivism. The Spanda Karika contains several significant commentaries, including a vritti by Kallata.