  The goal of this paper is to review some analytic techniques that are
potentially useful to shed light on the determinacy question that arises in New
Keynesian models as result of a combination of several monetary policy rules;
in these models, we provide conditions to guarantee existence and uniqueness of
equilibrium by means of results that are obtained from theoretical analysis. In
particular, these methods confirm the well known fact that Taylor--like rules
in interest rate setting are not the only way to reach determinacy of the
rational expectations equilibrium in the New Keynesian setting. The key
technical tool we use for that purposes is the so--called Budan--Fourier
Theorem, that we review along the paper. All the ideas and techniques presented
have been already used, our contribution that might be original here are the
organization and emphasis.
