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Introduction
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The Renormalization Group method has become one of the basic concepts in Physics, ranging from areas such as Quantum Field Theory and Statistical Mechanics to Condensed Matter Physics. The many interesting and relevant models encountered in these fields are usually not exactly solvable except for some privileged cases in one dimension. It is then when we resort to the RG method to retrieve the essential features of those systems in order to have a qualitative understanding of what the physics of the model is all about. This understanding is usually recasted in the form of a RG-flow diagram were the different possible behaviours of the model leap to the eyes.

Many authors in the past have contributed significantly to the idea of renormalization and it is out of the scope of this paper to give a detailed account on this issue here. We shall be dealing with the the version of the RG as introduced by Wilson [@wilson] and Anderson [@anderson] in their treatment of the Kondo problem, and subsequent developments of these ideas carried out by Drell et al. at the SLAC group [@drell] and Pfeuty et al. [@jullien].

It was Wilson in 