Language Change in East Asia, Thomas E. McAuley, Psychology Press, 2001, ISBN 978-0-7007-1377-6, ... Khitan and Tangut were anything but blips. They developed sophisticated literatures and were each used for a couple of centuries till their states were assimilated by the Mongols, and both were used for some time after ... The Tangut state of Xixia, for example, has left us with over six thousand documents/inscriptions, over half of which are Buddhist ...
