  The problem we consider is given a mixed model $F(\gamma) \rightarrow \gamma
\rightarrow \tilde{\gamma}$ and a potential $\widehat{V}$ such that $\log
\widehat{V} \in L^{1}$, to determine a movement $U$ such that $F(U
\gamma)=F(\gamma) + \widehat{V}$.
