  In previous publications dressed coordinates and dressed states has been
introduced. Specifically, a system composed by a harmonic oscillator
interacting linearly with an infinity set of other oscillators has been
treated. In this paper we show how to generalize such dressed coordinates and
dressed states to a nonlinear version of this system. Also we clarify some
misunderstandings about the concept of dressed coordinates. Indeed now we
prefer to call them renormalized coordinates to emphasize the analogy with the
renormalized fields in quantum field theory.
