w The ‘‘lock-in’’ model by Arthur Arthur, W.B., 1988. Competing technologies. In: Dosi, G., Freeman, C., Nelson, R., Ž . x Silverberg, G., Soete, L. Eds. , Technical Change and Economic Theory. Pinter, London, pp. 590–607. can be extended to the case of two and even three sources of random variation. Thus, one can model a triple helix of university–industry– government relations. In the case of...