... modelling

Previous versions of this paper and its companion were presented in seminars at ETH in the University of Zurich, the Science Policy Research Unit in the University of Sussex and the Complexity Discussion Group of the Centre for Policy Modelling and the Physics, Mathematics and other departments of the University of Manchester. Discussion in these seminars helped me enormously in developing the ideas reported here.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

...downing00.

For a review of the techniques employed by the pioneering researchers in the field, see Becu et al. (2003).

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.