求Heifner文献二篇（关于套期保值）,Google不到原文，向坛子里各位求助。急急急！！！
（1）Heifner, R. G. Hedging Potential in Grain Storage and Livestock Feeding. Washington DC: U.S. Department of AgricultureA gr. Econ. Rep. No. 238, 1973.
(2) Heifner, R. G. "Optimal Hedging Levels and Hedging Effectiveness in Cattle Feeding." Agr. Econ. Res. 24(1972):25-36.