In mechanism design with (partially) verifiable information, the revelation principle holds if allocations are modelled as the Cartesian product of outcomes and verifiable information, giving rise to evidence-contingent mechanisms. Consequently, incentive constraints characterize the implementable set. The revelation principle does not hold when an allocation is modelled as only an outcome so that mechanisms are non-contingent. Yet, any outcome implementable by an evidence-contingent mechanism is implementable by a non-contingent mechanism, provided it can both extend and restrict reporting information. A type-independent bad outcome implies the latter property.
revelation principle mechanism design verifiable information