The Converse Envelope Theorem
证明了包络公式等价于一阶条件，即逆包络定理；该定理无需选择集结构，可用于扩展机制设计中单调分配的可实施性，并应用于信息销售。
I prove an envelope theorem with a converse: the envelope formula is equivalent to a first‐order condition. Like Milgrom and Segal's (2002) envelope theorem, my result requires no structure on the choice set. I use the converse envelope theorem to extend to general outcomes and preferences the canonical result in mechanism design that any increasing allocation is implementable, and apply this to selling information.