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INTRODUCTION

Lepton scattering is one of the best ways to gain information on the quark substructure of nucleons and nuclei. The interaction of the electromagnetic probe with the quarks is well understood theoretically, and the relatively weak coupling allows for a clean separation of the scattering mechanism from the target structure. The weak coupling is especially important in probing nuclei, because the scattering is not strongly modified by additional interactions with the target. Leptonic probes have been used to make precise measurements of the polarized and unpolarized structure functions of the proton. The parton model predicts that at large momentum transfer, q, and energy transfer, $\nu$, the structure functions depend only on Bjorken-x [$x = (q^2-\nu^2)/2m_p\nu = Q^2/2m_p\nu$]. The structure functions measured in this limit can be directly related to the quark distributions within the nucleon, allowing one to extract polarized and unpolarized quark distributions within the proton. The same holds true for lepton scattering from nuclear targets. The structure function in the scaling limit can be related to the quark distributions in the nucleus. This not only provides information on the quark structure of nuclei, but is also our best method of obtaining information on the neutron structure function. Direct scattering measurements from neutrons are not feasible since neutron targets of adequate density are not available. Therefore, most of the information on (unpolarized) neutron structure comes from comparisons of the proton and deuteron structure functions. Extraction of the neutron structure function depends not only on precise measurements on the proton and deuteron, but also on the understanding of nuclear effects in the deuteron. The European Muon Collaboration (EMC) discovered [1] that the nuclear structure function is significantly different from the proton structure function, showing that these nuclear effects are non-trivial. Measurements of the EMC effect in light nuclei will provide guidance for modeling of nuclear effects in the deuteron, which must be understood to extract the neutron structure function. These measurements will also provide a testing ground for models that try to describe the EMC effect. In addition to extending measurements of the EMC effect to lighter nuclei, ³He and ⁴He measurements can be compared directly to microscopic calculations of nuclear structure which do not exist for heavier nuclei.