Lewis, David (1980), A Subjectivist's Guide to Objective Chance. In Richard C. Jeffrey (ed.), Studies in Inductive Logic and Probability, Vol. II. Berkeley: University of Berkeley Press, 263-293. Reprinted with Postscripts in David Lewis (1986), Philosophical Papers. Vol. II. Oxford: Oxford University Press, 83-132. pdf

Part I: pp. 83-98 (The Principle Reformulated)

Part II: pp. 98 (Chance and the Probability Calculus) -113

Further Reading:

Lewis, David (1994), Humean Supervenience Debugged. Mind 103, 473-490.