  The response of a nucleus composed of nucleons and confined quarks is
calculated in a non-relativistic cluster model and is shown to be a convolution
of responses of, respectively, a nucleus with interacting point-nucleons and of
a nucleon composed of quarks. We further show that the apparent off-shell
energy in the expression for the nucleon structure function in Impulse
Approximation does not constitue a real problem. We conjecture a generalization
to the relativistic regime.
