?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.au=Sigmund%2C+K.&rft.aulast=Sigmund&rft.aufirst=K.&rft.date=1995&rft.issn=1946-7087&rft.atitle=The+arithmetics+of+mutual+help&rft.title=Scientific+American&rft.pages=50-55&rft.genre=article