In unbounded subset $��$ in $R^n$ we study the operator $u\rightarrow gu$ as an operator defined in the Sobolev space $W^{r,p}(��)$ and which takes values in $L^p(��)$. The functions $g$ belong to wider spaces of $L^p$ connected with the Morrey type spaces. The main result is an embedding theorem from which we can deduce a Fefferman type inequality.

6 pages