  The carbon and nitrogen isotopic ratios of pre-solar SiC grains of type A+B
suggest a proton-limited nucleosynthetic process as encountered, for instance,
during the very late thermal pulse of post-AGB stars. We study the nuclear
processes during this phase and find carbon and nitrogen isotopic ratios which
can reproduce those of A+B grains. These results are still preliminary because
they depend on uncertain factors such as the details of mixing during the
post-AGB thermal pulse, the rates of some nuclear reactions, and the
assumptions on mixing during the progenitor AGB phase.
