@unpublished{publication-5807,
	author={Falk, Armin and Fischbacher, Urs},
	institution={University of Zurich},
	issn={1424-0459},
	number={No. 6},
	series={Working paper series / Institute for Empirical Research in Economics},
	title={A Theory of Reciprocity},
	year=2000,
}