@article {10109,
	title = {Numerical and analytical study of evolution of indirect reciprocity},
	journal = {Physica A: Statistical Mechanics and its Applications},
	year = {2002},
	pages = {683-694},
	doi = {10.1016/S0378-4371(02)00969-X},
	author = {Xiang Cheng and Qi Ouyang}
}
