ABSTRACT
The basic philosophy of any renormalization group theory is to describe the physics of the problem in terms of an effective Hamiltonian at each length scale which is expressed in terms of a small basis set of operators multiplied by coupling constants which depend upon the length scale. Following the notions of Kadanoff and Wilson, we imagine integrating out variables on small length scales to derive Hamiltonians on large length scales. The first to apply such concepts to the Kondo problem in a straightforward manner was Anderson (1970). Later this idea was formulated in the framework of the multiplicative renormalization group (Abrikosov and Migdal 1970, Zawadowski and Fowler 1970, Fowler and Zawadowski 1971). In this section, we wish to lay out some of the relevant concepts and terminology.
