2 Axelrod, R. (1984) ]The Problem of Cooperation[ Harper & Rowe p.10

3 Taylor, M. (1976) ]Anarchy and Cooperation[ John Wiley & Sons pp.31-32

4 Ritter, F. & Wallach, D. (1998) "Models of Two-person Games in ACT-R and SOAR" ]Proceedings of the Second European Conference on Cognitive Modelling[ Nottingham University Press pp.202-203

5 Axelrod, R. (1981) "The Emergence of Cooperation among Egoists" ]American Political Science Review[ 75, no.2 pp.320-321

6 See Traces.

7 For example, the matrix presented by Ritter & Wallach op.cit. p202

8 Campbell op.cit. pp.6-7