Environmental regulation of livestock production contracts by P. Bontems, Pierre Dubois and T. Vukina http://www.toulouse.inra.fr/centre/esr/wpRePEc/bon200406.pdf

对传统的模型Principal-Agent 模型有一个很好的改进，并在实证上进行了支持分析，

There are some innovations , both theoretically and empirically, I think.