  The SU($N$) principal chiral model is asymptotically free and integrable in
$1+1$ dimensions. In the large-$N$ limit, there is no scattering, but
correlation functions are {\em not} those of a free field theory. We briefly
review the derivation of form factors for local operators. Two-point functions
for such operators are known exactly. The two-point function of scaling-field
operators has the short-distance behavior expected from the renormalization
group. We briefly discuss non-vacuum operator products. The ultimate goal is to
derive the Lagrangian field theory from this axiomatic quantum-field-theory
formalism.
