C. Lange, M. Kerber, und C. Rowat. (2013)Tutorial at INFORMATIK 2013, Computer science adapted to humans, organization and the environment, 43rd annual meeting of the German Informatics Society (Gesellschaft für Informatik e.V. (GI)).
U. Menne. (2017)cite arxiv:1705.05253Comment: The present text is a version with additional references but without figures of a note compiled for the Notices of the American Mathematical Society. (v4: considerably expanded introduction, 6 pages).