  The calculation of neutrino decoupling from nuclear matter requires a
transport formalism capable of handling both collisions and flavor mixing. The
first steps towards such a formalism are the construction of neutrino and
antineutrino "distribution matrices," and a determination of the Liouville
equations they satisfy in the noninteracting case. These steps are accomplished
through study of a Wigner-transformed "density function," the mean value of
paired neutrino quantum field operators.
