Co-operative solutions to the Prisoner's Dilemma

For helpful comments, my thanks to Robert Bright, Richmond Campbell, Julia Colterjohn, Peter Danielson, Ish Haji, Keith Lehrer, Robert Martin, Victoria McGeer, Terrence Tomkow and an anonymous referee. I also thank the Canadian S.S.H.R.C. for a Doctoral Fellowship and Dalhousie University for a Killam Post-Doctoral Fellowship.