Kashmir Shaivism has been a nondualistic school, and is distinct from the dualistic Shaiva Siddhānta tradition that also existed in medieval Kashmir. A notable philosophy of monistic Kashmiri Shaivism has been the Pratyabhijna ideas, particularly those by the 10th century scholar Utpaladeva and 11th century Abhinavagupta and Kshemaraja. Their extensive texts established the Shaiva theology and philosophy in an advaita (monism) framework. The "Siva Sutras" of 9th century Vasugupta and his ideas about "Spanda" have also been influential to this and other Shaiva sub-traditions, but it is probable that much older Shaiva texts once existed.