1. Rare Breeds;Alderson,1994
2. Resource Conservation: Economics and Policies;Ciriacy-Wantrup,1968
3. Scale and feedback mechanism in market economics;Clark,1995
4. Cleo and the economics of QWERTY;David;American Economic Review,1985
5. FAO, no date. Extensive pastoral livestock systems: issues and options for the future. http://www.fao-kyokai.or.jp/edocuments/docement2.html