Indus Valley civilization (3rd/2nd millennium BCE), but this script – if it is a script – remains undeciphered. If any scripts existed in the Vedic period, they have not survived. Scholars generally accept that Sanskrit was spoken in an oral society, and that an oral tradition preserved the extensive Vedic and Classical Sanskrit literature. Other scholars such as Jack Goody argue that the Vedic Sanskrit texts are not the product of an oral society, basing this view by comparing inconsistencies in the transmitted versions of literature from various oral societies such as the Greek, Serbian, and other cultures. This minority of scholars argue that the Vedic literature is too consistent and vast to have been composed and transmitted orally across generations, without being written down. Lipi is the term in Sanskrit which means "writing, letters, alphabet". It contextually refers to scripts, the art or any manner of writing or drawing. The term, in the sense of a writing system, appears in some of the earliest Buddhist, Hindu, and Jaina texts. Pāṇini's Astadhyayi, composed sometime around the 5th or 4th century BCE, for example, mentions lipi in the context of a writing script and education system in his times, but he does not name the script. Several early Buddhist and Jaina texts, such as the Lalitavistara Sūtra and Pannavana Sutta include lists of numerous writing scripts in ancient India. The Buddhist texts list the sixty four lipi that the Buddha knew as a child, with the Brahmi script topping the list. "The historical value of this list is however limited by several factors", states Salomon. The list may be a later interpolation. The Jain canonical texts such as the Pannavana Sutta – probably older than the Buddhist texts – list eighteen writing systems, with the Brahmi topping the list and Kharotthi (Kharoshthi) listed as fourth. The Jaina text elsewhere states that the "Brahmi is written in 18 different forms", but the details are lacking. However, the reliability of these lists has been questioned and the empirical evidence of writing systems in the form of Sanskrit or Prakrit inscriptions dated prior to the 3rd century BCE has not been found. If the ancient surface for writing Sanskrit was palm leaves, tree bark and cloth—the same as those in later times, these have not survived. According to Salomon, many find it difficult to explain the "evidently high level of political organization and cultural