2005/09/13 by Alexander A. Chernitskii
Physics and Astronomy · #hep-th
published as Encyclopedia of Nonlinear Science, ed. Alwyn Scott. New York and London: Routledge, 2004, pp. 67-69 · 4 pages, Internet address for Encyclopedia of Nonlinear Science is http://www.routledge-ny.com/ref/nonlinearsci/
arxiv created 2005/09/13 · arxiv updated 2009/12/01
Electronic version of Entry in Encyclopedia of Nonlinear Science.