  Single pion leptoproduction in the region of the (3,3) resonance is currently
of high interest for at least two reasons: (i) These reactions constitute an
important part of the total cross section in low energy reactions and are
utilized to detect neutrino oscillations in current and future long baseline
experiments. (ii) Intranuclear rescattering of the pions in heavy nuclei
results in interesting and sizable modifications of the free nucleon cross
sections which are testable in electroproduction experiments. In this article
we give a basic introduction to the pion multiple scattering model of Adler,
Nussinov, and Paschos (ANP) with special emphasis on pion absorption. We also
estimate the probability of multiple scattering.
