1. D. Ruelle, The Mathematical Intelligencer 2 (1980) 126
2. J.D. Farmer, E. Ott and J. Yorke, Physica 701 (1983) 153
3. J.D. Farmer in “Evolution of Ordered and Chaotic Patterns in Systems treated by the Natural. Sciences and Mathematics”, ed. H. Haken, ( Springer, Berlin 1983 ) p. 228
4. J.C. Antoranz and M.G. Velarde in “Nonequilibrium Cooperative Phenomena in Physics and related Fields”, ed. M.G. Velarde, ( Plenum 1984 ) p. 103.
5. Most information in this review, also as regards theory, is contained in papers by other authors in Proceedings of the 59th Nobel symposium, June 1984, published as Physica Scripta 19 (1985), ed. S. Lundqvist.