  The Maskin's theorem is a fundamental work in the theory of mechanism design.
In this paper, we propose that if agents report messages to the designer
through channels (e.g., Internet), agents can construct a self-enforcing
agreement such that any Pareto-inefficient social choice rule satisfying
monotonicity and no-veto will not be Nash implementable when an additional
condition is satisfied. The key points are: 1) The agreement is unobservable to
the designer, and the designer cannot prevent the agents from constructing such
agreement; 2) The agents act non-cooperatively, and the Maskin mechanism remain
unchanged from the designer's perspective.
