Weizsacker, E. v., Lovins, A. B., Lovins, H. L. ., Lovins, A. B., & Lovins, L. H. (1997). Factor four: Doubling wealth, halving resource use: the new report to the Club of Rome. London: Earthscan Publications LTD.

Weizsacker, Ernst von, Amory B. Lovins, Hunter L. Lovins, Amory B. Lovins, and L. Hunter Lovins. Factor Four: Doubling Wealth, Halving Resource Use: The New Report to the Club of Rome. London: Earthscan Publications LTD, 1997.

Weizsacker, Ernst von, et al. Factor Four: Doubling Wealth, Halving Resource Use: The New Report to the Club of Rome. London: Earthscan Publications LTD, 1997.