  We present and discuss correlations for optical and near-infrared (5500-10030
angstroms) line intensity measurements at many positions in the Crab Nebula.
These correlations suggest the existence of gas produced by a range of nuclear
processing, from material in which synthesis ended with the CNO-cycle, to some
helium-burning and nitrogen depletion, to regions containing enriched products
of oxygen-burning. The latter exhibit a gradual, linear rise of [Ni II]
emission with increasing argon enrichment, whereas gas with less nuclear
processing shows markedly different [Ni II] emission characteristics, including
the highest derived abundances. This suggests two origins for stable,
neutron-rich nickel in the nebula: a type of "alpha-rich freezeout" in the more
highly processed material, and possibly removal of ions from the neutron star
in other regions. In addition, the data indicate that anomalously strong
observed [C I] emission comes from broad, low-ionization zones. Although the
strongest He I emission could also be enhanced in similar low-ionization gas,
correlations between relevant line ratios argue against that interpretation,
strengthening the case for an exceptionally high helium mass fraction in some
locations.
