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Structural models with no solution are incoherent, and those with multiple solutions are incomplete. We show that models with occasionally binding constraints are not generically coherent. Coherency requires restrictions on the parameters or on the support of the distribution of the shocks. In presence of multiple shocks, the support restrictions cannot be independent from each other, so the assumption of orthogonality of structural shocks is incompatible with coherency. Models whose coherency is based on support restrictions are generically incomplete, admitting a very large number of minimum state variable solutions.

We estimate a medium-scale model with and without rule-of-thumb consumers over the pre-Volcker and the Great Moderation periods, allowing for indeterminacy. Passive monetary policy and sunspot fluctuations characterize the pre-Volcker period for both models. In both subsamples, the estimated fraction of rule-of-thumb consumers is low, such that the two models are empirically almost equivalent; they yield very similar impulse response functions, variance, and historical decompositions. We conclude that rule-of-thumb consumers are irrelevant to explain aggregate U.S. business cycle fluctuations.

We show how to use Hurwitz polynomials to study the stability and uniqueness of Rational Expectation equilibria in Dynamic General Equilibrium models. We apply this method to a model characterized by staggered wage and price contracts and by limited asset market participation (LAMP). We prove analytically in a fourth-order dynamics system that, once nominal wage stickiness is taken into account, LAMP does not invalidate the Taylor Principle: for any plausible degree of asset market participation an active interest rate rule ensures the uniqueness of the rational expectation equilibrium.

We consider a simple, self-financing and informationally undemanding scheme to reduce the deadweight loss due to a monopolist's market power. Essentially, we propose taxing the monopolist and applying the tax revenue to generate a public demand for his output. It turns out that a favorable scenario for such a reform to generate an ‘efficiency increase’ (i.e. to increase total output) is an elasticity of market demand with an absolute value of less than 3 (a seemingly ‘realistic’ condition). We also consider the case for the implementation of the first best, and compare specific and ad-valorem taxes as a way to finance the public demand.