  We discuss a new approach to final state interactions, that keeps explicitly
into account the virtuality of the ejected nucleon in quasi-elastic $A(e,e'p)X$
scattering at very large $Q^2$, and we present some recent results, at
moderately large $Q^2$ values, for the nuclear transparency in $^4He$, $^{16}O$
and $^{40}Ca$ and for the momentum distributions of $^4He$.
