Casti, J. <https://pure.iiasa.ac.at/view/iiasa/1179.html>  (1984).  On the theory of models and the modelling of natural phenomena.    In:  On the theory of models and the modelling of natural phenomena. Eds. Bahrenberg, G., Fischer, M., & Nijkamp, P. <https://pure.iiasa.ac.at/view/iiasa/2236.html>, pp. 73-92 Gower.  ISBN 978-0566006852