Casti, J. <https://pure.iiasa.ac.at/view/iiasa/1179.html> & Swain, H. <https://pure.iiasa.ac.at/view/iiasa/2436.html>  (1975).  Catastrophe theory and urban processes.    In:  Optimization Techniques Modeling and Optimization in the Service of Man Part 1. Eds. Cea, J., pp. 388-406 Germany: Springer Berlin Hiedelberg.  ISBN 978-3-540-38144-0 10.1007/3-540-07622-0_483 <https://doi.org/10.1007/3-540-07622-0_483>.