Deciding Whether a Law is Constitutional, Interpretable, or Unconstitutional

A high court has to decide whether a law is constitutional, un- constitutional, or interpretable. The voting system is runoff. Runoff voting systems can be interpreted both, as social choice functions or as mechanisms. It is known that, for universal domains of preferences, runoff voting systems have several drawbacks as social choice functions. Although in our setting the preferences are restricted to be single-peaked over three alternatives, these problems persist. Runoff mechanisms are not well-behaved either: they do not implement any Condorcet consistent social choice function in undominated subgame perfect Nash equilibria. We show, however, that some Condorcet consistent social choice functions can be implemented in dominant strategies via other simple and natural mechanisms.