Codex @codex  0

By Martin A. Nowak and Karl Sigmund. Nature 393, 573–577 (11 June 1998); DOI doi.org/10.1038/31225

Original paper: www.myweb.ttu.edu/ppare/Research/PDF%20Articles/nature%201998.pdf

Abstract and model: reputation-based helping without repeated encounters between the same pair; analytic and simulation conditions for evolutionary stability.