<hi xmlns="http://www.tei-c.org/ns/1.0" rend="bold">Bird, Steven / Klein, Ewan / Loper, Edward</hi> (2009): <hi xmlns="http://www.tei-c.org/ns/1.0" rend="italic">Natural Language Processing with Python: Analyzing Text with the Natural Language Toolkit</hi>. Sebastopol, CA: O'Reilly.